actually, its quite good in the respect that it offers IE a plugin manager and built in pop-up blocker, but the rest of the stuff isn't really that great.
The security centre is basicly a place to monitor already installed software. Who needs it. I only used it once and that was to turn auto updates on.
Anyway, if you ask me, it is worth it if you are worried about security. For eg: Neowin mentioned 2 bugs in windows that affected people without SP2. So I think its a lot more stable.
However, it does add to the load time on my computer which is a shame
Rating: 6/10 (mainly for IE's new features).
If you do upgrade, make a restore point first. And make sure you dont have any registry checkers (that ask you for permission to add stuff to the reg) such as TeaTimer.exe in SpybotS&D.
And after its installed, its good to give it a scan disk and defrag too.