I spotted a reference on John Nack's blog (one of the Lightroom development team) to this
site. This guy has used the SDK in Lightroom 1.3 to produce export modules for Flickr, Smugmug and Zenfolio (not familiar with this). Although they're still beta and clearly have some rough edges, I took the link from Nack's blog as a bit of an endorsement and based on some fairly rudimentary testing (Flickr only), I'm quite impressed.
I think I can also fairly safely say, that there is no obvious risk to experiment here - in the worst case, just delete the folder - but form your own judgement and 'caveat emptor'.