Uses
The following uses for gold are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).
Gold has been used for centuries for jewellery and decoration. In addition to the more familiar rings, brooches, necklaces, and ear rings, gold is used as gold leaf for decoration and protection, screen printing (directly on to bone china, earthenware, porcelain, and glass surfaces or decals). Gold is the key component for "liquid gold", preparations containing up to 12% gold ideal for decorative application using brushes and gold pastes used for screen printing. The UtiliseGold directory contains many links to gold suppliers and products for these gold applications and those outlined below.
Gold is also well known as a coinage metal (because of its scarcity, inertness, and decorative features) and is a standard for monetary systems in many countries. Apart from gold coins, gold ingots, and gold bars, gold is available in many forms including pure gold and alloys as gold flakes, foil gauzes (meshes), grain, powders, sheet, sponges, tubes, wires and even single gold crystals.
Recently, gold catalysts as gold supported on carbon or metal oxides are becoming useful in the chemical industry. Many other gold compounds including neutral gold halides (AuBr3, etc.), aurates (K[AuBr4], etc.) gold cyanides, gold oxides, phosphine gold complexes, gold hydroxides and gold nitrates are available to industrial users. Chlorauric acid (HAuCl4) is used in photography for toning the silver image.
Gold is a really useful metal for electronics because of its inertness and physical properties. Gold is used for electrical contacts, spring contacts, bonding wire, solder alloys, bonding wire, bumping wire, electroplating, and sputtering targets. Gold is also a useful brazing material. Gold is used for coating space satellites, as it is a good IR reflector and is inert.
Since gold is inert and possesses useful properties when alloyed, gold is used extensively for dentistry in gold teeth, dental attachments, inserts, and solders. Similarly, gold is used increasingly for medical implants in eyes and ears, as well as many other medically useful wires, tubes, sheets, and foils. Disodium aurothiomalate is administered (intramuscular) as a treatment for arthritis. The gold isotope 198Au is used for treating cancer and other conditions.
Gold is used in nanotechnology applications as colloids, conjugates, nanoparticle inks, nanoparticle solutions, and nanopowders.

Geological information
Abundances
In this table values are given in units of ppb (parts per billion; 1 billion = 109), both in terms of weight and in terms of numbers of atoms. Values for abundances are difficult to determine with much certainty, so all values should be treated with some caution, especially so for the less common elements. Local concentrations of any element can vary from those given here by orders of magnitude.
Abundance   ppb by weight           ppb by atoms
Universe        0.6      0.004
Sun     1          0.01
Meteorite (carbonaceous)             170     20
Crustal rocks            3.1      0.3
Sea water      0.05    0.0016
Stream           0.002 0.00001
Human           100     3

Notes
Gold is found as the free element in nature and associated with quartz, pyrite and other minerals. Two thirds of the world's supply comes from South Africa. Much of the USA production is from the states South Dakota and Nevada. Gold is found in sea water (about 5-6 g in a million tonnes of seawater), but no effective economic process has been designed (yet) to extract it from this source.

Historical information
Discovered by:         Known since ancient times.
Discovered at:          not known
Discovered when:   no data         
Origin of name:        From the Anglo-Saxon word "gold" (the origin of the symbol Au is the Latin word "aurum" meaning "gold")
Notes
Gold was known and highly valued from earliest times. Egyptian inscriptions dating back to 2600 B.C. describe gold and gold is mentioned several times in the Old Testament.
Gold is one of the elements which has an alchemical symbol, shown below (alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold).
Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for gold is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Gold has been the basis of many currencies over the centuries and so for economic reasons, among others, the possession of gold was or is restricted in some countries. Notably, private ownership of gold (apart from as jewelry and coins) was banned between 1933 and 1975.

Biological information
Biological role
Here are a few notes about the biological role of gold.
Gold has no biological role but does form the basis of some drugs (possibly toxic) used to treat rheumatoid arthritis. Its mode of action appears not to be understood.
Levels in humans
The following gives the abundances of the elements in humans.
            Human abundance [/ppb by weight]: 100
            Human abundance [/atoms (C = 1000000)]: 3

Hazards and Risks
Here are a few notes about the hazards and risks associated with gold.
Gold is not absorbed well by the body and its compounds are not normally particularly toxic. Up to 50% of arthritic patients treated with gold-containing drugs may show toxic effects however resulting in damage to the liver and to the kidneys.

Chemical reactions of the elements
Reaction of gold with air
Gold metal is stable in air under normal conditions. However gold does dissolve in aqueous cyanide solutions in the presence of air.
Reaction of gold with water
Gold does not react with water.
Reaction of gold with the halogens
Gold metal reacts with chlorine, Cl2, or bromine, Br2, to form the trihalides gold(III) chloride, AuCl3, or gold(III) bromide, AuBr3, respectively. On the other hand, gold metal reacts with iodine, I2, to form the monohalide gold(I) chloride, AuI.
2Au(s) + 3Cl2(g) → 2AuCl3(s)
2Au(s) + 3Br2(g) → 2AuBr3(s)
2Au(s) + I2(g) → 2AuI(s)
Solutions of chlorine, Cl2, and trimethylammonium chloride, [NHMe3]Cl, in acetonitrile, MeCN, dissolve gold.
Reaction of gold with acids
Gold metal dissolves in aqua regia, a mixture of hydrochloric acid, HCl, and concentrated nitric acid, HNO3, in a 3:1 ratio. The name aqua regia was coined by alchemists because of its ability to dissolve gold - the "king of metals".
Reaction of gold with bases
Gold does not react with aqueous bases.
Binary Compounds
This section lists some binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and some other compounds of gold. For each compound, a formal oxidation number for gold is given, but the usefulness of this number is limited for p-block elements in particular. Based upon that oxidation number, an electronic configuration is also given but note that for more exotic compounds you should view this as a guide only. The term hydride is used in a generic sense to indicate compounds of the type MxHy and not necessarily to indicate that any compounds listed behave chemically as hydrides.
In compounds of gold (where known), the most common oxidation numbers of gold are: 3.

Hydrides
The term hydride is used to indicate compounds of the type MxHy and not necessarily to indicate that any compounds listed behave as hydrides chemically.
    * none listed
Fluorides
    * AuF3: gold (III) fluoride
    * AuF5: gold (V) fluoride
Chlorides
    * AuCl: gold (I) chloride
    * [AuCl3]2: gold (III) chloride
    * Au4Cl8: gold (I, III) chloride
Bromides
    * AuBr: gold (I) bromide
    * [AuBr3]2: gold (III) bromide
Iodides
    * AuI: gold (I) iodide
    * AuI3: gold (III) iodide
Oxides
    * Au2O3: gold (III) oxide
Sulfides
    * Au2S: gold (I) sulphide
    * Au2S3: gold (III) sulphide
Selenides
    * AuSe: gold (I, III) selenide
    * Au2Se3: gold (III) selenide
Tellurides
    * AuTe2: gold ditelluride
Nitrides
    * none listed
Carbonyls
    * none listed
Complexes
    * none listed
NMR data