I had an acceptance call from a Yale professor this morning. Great surprise, since I didn't hear anything from them yesterday and have been rejected from Northwestern, which I thought had a better chance both in terms of perceived fit and competitiveness. I hope you hear a good news soon!
I'm not planning on "negotiating" at all, but how on earth can they rescind offer when they can just say no to more money? Once they made an offer, they can't rescind it without particularly valid and exceptional reasons (i.e. plagiarism, falsified application).
I have been accepted to UC Berkeley and it is absolutely my dream school, but I can't not be concerned with the budget situation there... could the guaranteed five-year funding be endangered if the situation gets really dire in the next few years? (the latest: http://www.bizjournals.com/sanfrancisco/news/2011/02/07/uc-berkeley-could-take-80m-hit-in.html)