I finally decided to switch to KDE4.1 for my every day use as DE on linux. The compilation and installation went smooth, but there are some outstanding performance problems with the nvidia drivers 
Transparency, wobbly windows and scrolling works ok. Resizing windows and switiching virtual desktops takes somewhere between 0.5 to 2 seconds. Something is very broken in the graphics stack on linux/X11/nVidia setups, and as far as I understand it, most of the blame lies with nVidia’s drivers.
I get a rather high cpu usage from kwin (about 30% on core) and i get significantly lower ’score’ in glxgears. I get around ~3500 fps vs ~5000 fps on kde3.5.
Would be interesting to see how kde4.1 performs on OpenSolaris or FreeBSD with nvidia graphics.
I generally like kde4, so I can live with the delays from bad drivers, and I’m excited about all the new ideas kde4 brings to the table.
