I have my beastly desktop, which is dual boot, one for the kids that is locked down with group policy out the yin-yang, a laptop running Vista and one running XP Pro. Some of the software I use is optimized for XP (VMWare, etc.). VMWare especially hates how Vista uses all of the memory on the system for cache and doles it out as it sees appropriate.
Plus you need two laptops…so that assholes that forget theirs can join your game of StarCraft.
And I.E…? Wow…