We recently shipped Expression Blend, the product I had been working on for the last few years.  I love the product and the team, but it was the longest project I've ever worked on, and I was offered a great new opportunity:  to work on WPF, both the desktop version we shipped with Vista and the new Silverlight component.  The work isn't that vastly different.  From many years working with the WPF team, I know most people very well already.  I go to many of the same meetings, just sit on a different side of the room.  But of course there are still those vast areas, little things about the new team, of which I am completely ignorant.  Which is what I wanted:  to learn a lot of new stuff.  Be careful what you ask for, as they say.