I suspect both are playing a role, but I think recent KDE optimizations might be most responsible.
The Beta 1 release seemed to have horribly slow maximizing, but that is no longer the case.
I think one of the features in 185.18.10 and newer is allowing small pixmaps to be stored in video memory on 8000 series cards. IMO it seemed to make things more responsive as far as switching between, minimizing, and maximizing browser windows, could just be me though.
There is a new social-desktop widget and I'm giving it a spin. I think it's work in progress, but interesting potential. Seems like it's going to be some sort of cross between social-networking and instant messaging, integrated right in to the desktop.
Lets you create a profile, join groups, add friends, and get a list of other users who are close to your longitude and latitude... Seems pretty cool so far.