I have been using Microsoft Windows Vista Ultimate 64-Bit for more than a month and I must say I am pretty comfortable with it. Even though not much changes from Windows XP besides the GUI, it supports DirectX 10 which is a must have for all gamers.
Till now, I have gotten only 1 Blue Screen of Death (BSOD) when I am upgrading to the Windows Vista 64-bit service pack 1. Since then, I have not gotten a single crash *TOUCH WOOD*.