IE9 is Windows 7 only - I NEVER upgrade OS's until they have gone thru 2-3 Service Packs, so I will use XP until probably early 2013 ...
No offense, but that is a rather arbitrary criteria. Windows 7 came out 2 years ago and is just fine on systems that can run it. If the real issue is an older computer without the necessary hardware to run newer software, then you stick with what runs well on it, not claim that Win 7 hasn’t had all the bugs shaken out yet (never going to happen for any Windows version, even XP).
Win7 has already gone through 2 service packs and is virtually glitch free....been using it since I got my M11x and have grown to really like the platform. Might want to consider moving from XP to Win7 simply because Win7 uses RAM and such more effectively/efficiently.