As of today, Microsoft is offering Office and Vista to customers... and oh so very soon, Exchange 2007 will be available as well. I've been running all 3 for well over a year, and I can't imagine going back.
If you're interested in following the launch event, tune in to one (or both) of the following:
I promise to write more when we're done with E2K7... oh so very soon. In the mean time, feel free to pre-register for Exchange 2007 Eval here: http://www.microsoft.com/exchange/eval