The main problem with facebook as a search engine is that you need to be a member and you can only search in facebook. The great thing about the twitter realtime search is that you can actually just search right on their front page.<p>Another downfall of facebook realtime search for me and well for plenty of people I know is that facebook is blocked at my work so I will never use it, I don't use facebook now, though I do have a profile, but its not a good enough feature to bring me back to using it again.