Organometallic chemistry - the chemistry of compounds with metal-carbon bonds - is the basis of homogeneous catalysis. Metals enable transformations of organic substrates that would otherwise be hard to accomplish. Through the use of properly tuned ligands, one can achieve amazing rates and selectivities. Even nature uses metals for its more difficult enzymatic reactions.
Organometallic chemistry differs from inorganic and coordination chemistry in that it (usually) involves strong, covalent metal-carbon bonds. The main difference with organic chemistry is the polarity of the metal-carbon bond: whereas most "organic" C-X bonds have carbon on the positive end of the dipole, organometallics usually have a negative charge on carbon, leading to very different reactivity patterns. Transition metals, which have valence d-orbitals, also introduce new bonding and reactivity.
As a practical point, most organometallic complexes are sensitive to air and moisture (some even ignite spontaneously in air!). Handling them requires the use of glove boxes or specially designed glassware. Nevertheless, they have become so important that they are used on a large scale in industry.
Very few organometallic complexes are "end products". They are more often used as intermediates in organic synthesis or as catalysts in homogeneous catalytic reactions.