HubMed's unAPI export has a new option: del.icio.us. Selecting this option will post the article to del.icio.us with all the citation metadata encoded as machine tags, which are supported by Flickr now and hopefully will be supported by del.icio.us in the future...
Here's an example. The trouble at the moment is that the tags are getting cut off, because the field isn't long enough. Also, machine tags aren't kept separate, which is messy.
See also: Jon Udell: del.icio.us is a database.