The first news I've see today after my week of holiday is the big list of programs with possible issues in Service Pack 2 published by Microsoft here.
I've not installed XP SP2 at the moment but I'm really worried about the amount of software that can have problems (also Visual Studio .NET is included 
). I hope that the main amount of problems will be caused by the new firewall settings (ON by default), so they can be switched easily, otherwise I think it could be a serious problem. Only trying the new SP2 will say us if there will be real problems or not.
However, I'm not totally satisfied about the new Windows Firewall... ok, it's a good firewall if you consider the previous version of Windows Firewall on XP, but I think it's not complete like other products. Personaly, I' m using the free version of ZoneAlarm Firewall on my work pc, and it's more complete than the new XP Firewall.
For example, with ZoneAlarm you have an easy total control of the Firewall settings, you can easily turn on and off some Firewall's options, and expecially it includes the feature that only allows authorized programs to access the Internet. Why the new Windows Firewall don't have this feature?? 
It only filters incoming traffic... and the outbound traffic???
Mmm... not so good as I was expecting!