Can't say I've noticed much difference, I don't use IE so I don't know about the popup stopper.
Don't use the firewall either, so I don't know about that either.
The Security Center is extremely annoying, kept popping up little reminders that I had the firewall disabled, and apparently it didn't like AVG either since it kept complaining about it.
Overall, once I shut down the SC and some other new junk, it's pretty much like Sp1, so I figure, why not?
Oh and one thing, on every computer that I installed it on, Media Player got screwed up.
The ones that are fresh installs with Sp2 slipstreamed work fine though.