Windows 7 is worlds better in every way than XP. It does everything good that XP did, none of the bad, and it added a whole lot more that was missing and needed. It's even more rock solid. My computers run 24/7 and almost never get rebooted.
My day job is in Information Technology Services at a University, maintaining 2200 computers from the last 6 years. Initially, we thought the older P4 computers with 1GB of RAM wouldn't run 7. It turns out, though, that Windows 7 is actually faster on them than XP was. Even though Windows 7 does use more RAM than XP, it has far better virtual memory optimization and runs much better than XP ever could on limited RAM.