Still in school? Research librarian? Writer? Teaching bibliographic instruction? Then you may want to check out Zotero, a nifty download that works with Firefox (and Netscape Navigator 9 and some versions of Flock) to keep track of your research sources. Zotero captures citation information, allows tagging, saves searches, exports formatted citations, saves and searches, allows note taking, and more. It's free and open-source, so expect changes, additions, and updates along the way.
I remember giving myself a crash-course in EndNote for a huge bio-bibliography I did on Kate Chopin - I think this project would have been easier with a tool like Zotero. Very cool.