I asked that recently on Quora http://www.quora.com/Twitter-com-2010-Redesign/Why-did-they-use-!-as-the-permalinks-in-the-new-Twitter http://www.quora.com/Twit

I asked that recently on Quora http://www.quora.com/Twitter-com-2010-Redesign/Why-did-they-use-!-as-the-permalinks-in-the-new-Twitter http://www.quora.com/Twitter-com-2010-Redesign/Why-did-they-... There, a Twitter employee confirmed that they used the hashbang to comply with Google's proposal.