OK, so it's early days yet and anything can change, so this is absolutely not the final word, but several months ago when playing with early Windows Vista builds, I was encouraged that fast user switching on domain-joined Windows Vista machines with Media Centre (center) was possibly on it's way. It looks like that reality is getting one step closer with the marketing folks acknowledging this as a possible offering following a series of discussions I had yesterday. Keep watching and hopefully you'll see more as the next CTP build is released, hopefully very soon.