I've been using SP2 and Qwix for ages, no problems related to SP2 at all.
However, when I first UPGRADED to SP2 it completely messed up my machine. I had to reinstall completely. But a fresh install with SP2 either integrated, or applied immediately, is fine. If you install the apps after, it's fine. It's only the UPGRADE that causes REAL problems.
Some software is just incompatible with SP2 (like MS CRM for instance! - until they released some patches...fools
Qwix is cool tho.