I encourage people that can afford a new platform (read as additional to their production machine) to go ahead and play with Vista. It stands to reason that most are going to have to live with Vista for years to come. However, if you are productive on XP and have no experience with Vista and need to remain productive, DO NOT change your only machine over to Vista.
My opinion is from bringing up Vista on a Core 2 Duo machine and trying to live with it. I spent several hours fighting the built in security until I just resorted to turning off all that I could. Anyway it is an experience that makes OSX a pleasure to work with.
My opinion.
Neil