Those of you on the bleeding edge of reference management technology will know all about Connotea. It lives on your Firefox bookmarks toolbar, ready to spring into action whenever you come across a reference or website on the interweb you would like to save for later. You could think of it as a somewhat geeky social networking tool–you upload citations of interest and tag them, others do the same. You show them yours, and they show you theirs! Unless you mark yours as private, that is.
It is nice that it is free, but not so nice that you have to add each reference separately, you cannot, say, go to a bibliography page of a study (in a pearl growing attempt) and add them all in one batch. It is also great that it talks to Reference manager, Endnote, Word (it sends an .xml file that can be made into a bibliography), etc. This little gadget could make grey literature searching a whiz–or at least take the cut-and-paste drudgery out of it.
Oh, and no abstracts are included, if they are available. Another big caveat, but it should be easily solved by adding that functionality (hint, hint).