Scaling any window is extremely slow: Vertical, horizontal, or both. In fact, at its worst, it seems to lock up the entire system sometimes until it's done. Usually it's a 2-3 second delay.
I'm running KDE with Beryl; same thing happened with Compiz.
Specs:
intel quad core
nvidia 8600 gts
2 GB
All other window operations are instant: min, max, shade, etc...
