ChemSpider (1) now provides free web services to inter-convert molecular formats, including a look-up for InChIKeys. These are available either with a manual (2) or API interface (3).

Wikipedia describes the InChIKey (4):

The condensed, 25 character InChIKey is a hashed version of the full InChI (using the SHA-256 algorithm), designed to allow for easy web searches of chemical compounds. Most chemical structures on the Web up to 2007 have been represented as GIF files, which are not searchable for chemical content. The full InChI turned out to be too lengthy for easy searching, and therefore the InChIKey was developed.

Essentially InChIKeys are a way of representing organic molecules with a unique text string, no matter how large. Search engines like Google have no trouble indexing InChIKeys. Other text representations have been problematic. Molecules may be represented by multiple SMILES (5) and InChIs (6) can become too long for proper indexing.

In order for InChIKeys to be usable, it is necessary to be able to inter-convert them with other formats. These new web services make this process much easier.

If InChIKeys are systematically used as tags (7) on the open web, it will make it much easier to track the chemistry being reported using automated means.