Erm not really
started off with xp x64, ran it quite nice for well since it came out, then got given vista x64 home pro for free, so installed it
I use XP for gaming and the vista ultimate on the "test" rig part of the pc,
my solution was simple, have dual boot on his pc, have the XP and vista in the set up, if he dont like vista a simple format will cure it, this system aswell wont cost him anything as you can run vista for 30 days as a test anyway (without inserting a serial), if he dont like it he aint lost owt has he?
apart from the occasional driver issues , at the start, ive had no problem with vista at all, but as time goes on things bet better.
and everything is free, you just have to know where to look :)