Upgraded from XP MCE to ultimate (I needed media centre and remote desktop) on my main box, both the laptops had vista premium upgrades which arrived this week. Also upgraded my box at work to Vista business.
Loving it and not looking back - only slight issue I had was the packard bell upgrade for sue's laptop, it reckoned it could do an upgrade, so I backed up sue's stuff to the external HDD before as a precaution and went ahead, it took three hours and the upgrade utility from PB had left something incompatible on there and so it BSOD'd on bootup. I slapped the vista disk in, removed the partition, installed a clean copy (always my preferred scenario) and not had a single problem.