Zotero is a firefox extension that allows collection and management of citations. I downloaded and tried it and I like it for the very reason that it creates formatted citations (for inclusion in articles) automatically! WOW!. For once, I don't have to spend time on creating and formatting citations manually. For now, the tool does not yet have any support for sharing citations but that's on its way. I tried Nature's Connotea but was disappointed with what it offers, especially, in the case of knowledge discovery. It could be a useful tool though for "communities of practice" to share information when compared to del.icio.us.