How widespread is the .NET framework?

Question

Does anyone have any figures on how many people have the .NET framework installed. Is it wise to develop games/applications using the .NET framework if targeting home users (i.e. not IT professionals)? The reason I'm asking is of course that many users might be reluctant to install the thing just to run the game/application I've developed. P.S. Does the .NET framework ship with the upcomming Windows XP SP2? Thanks, Johan Tibell