I upgraded my Windows Vista Ultimate game system to Windows 7 Ultimate this weekend. Overall the system feels faster and I like the new taskbar. I really like the "snaps" feature that allows you easily tile two windows together.
What I didn't like was they took away the Aurora screen saver - it was my favorite of any platform. Luckily I found it online.
My CPU doesn't support hardware virtualization so I can't run XP mode; oh well.
The upgrade took about four hours.