Microsoft: Vista to be available until 2011, officially
Microsoft responded quickly with the official word: they haven't decided yet when to pull the pin on Vista. According to internal policy, operating systems are made available until at least four years after their introduction. In Vista's case, that would put the earliest date at January 2011.
Historically, Microsoft has allowed about a six month licensing overlap when a new OS is released. Pulling Vista prior to that amount of time could be a colossally bad PR move, as it would no doubt be interpreted as yet another sign that even Microsoft didn't think Vista was all that hot.
As far as Windows updates are concerned, consumer editions will stop receiving "mainstream updates" after April 10, 2012 (you'll still get security patches). Here's another small slap in the face to anyone who ponied up for Vista Ultimate: that includes you, too. Vista Business - though much less expensive to license - will be fully supported for an additional five years.