KDE 4.6 / Mesa 7.10 appear to run slightly faster than KDE 4.5 / Mesa 7.9, which is pretty nice in itself. The rest of the changes are mostly cosmetic, as far as day-to-day use is concerned.
I can also confirm every single issue reported by RealNC. Some of those, like the "minimize effect heading towards the wrong part of the screen" also existed in 4.5, which is a pretty weaksauce showing. I'd love it if the developers took made some effort to tie up some of those issues. They may be relatively minor, but they do mar the user experience.
No real complaints otherwise.