I upgraded to Win 7 on my 5 year old Thinkpad and now it runs faster! (Maybe it was the memory upgrade
). XP's time is up. It's a security risk compared to the advancements in Windows 7. The main reason it's around (notably in businesses) is legacy application compatibility; otherwise Microsoft would have pulled the plug earlier. However consider how many large companies have an installed base of XP (even the government) and Microsoft gets LOTS of pushback when they hint at ending support for a particular product. It's a tough line to walk.
I just bought a new 24" iMac 2 months ago to replace my 5 year old G5 based iMac. The G5 ran so well and you rarely had to futz with it which is great when you work in the tech industry supporting these things and the last think you want to do is come home and be the 'help desk' for your other users in the house (read significant other).
If you have an XP computer I'd run it till it drops (or make a plan to retire it) and then buy new hardware with Win 7. Yes the migration from XP to Win 7 isn't an easy task but that tells you how much has changed (for the good) under the hood.