The real problem with these is degraded performance with your monitor. I've got the OmniCube mentioned above, but this hasn't just been my experience w/r/t that, but with all sorts of these things. (Belkin's just happen to be the best.) However, my monitor gets fuzzy when I use this, like it's passing through too much. I've noticed this problem, though, with every KVM I've seen.

This isn't really a problem except during intense staring at my screen for hours or other graphics-oriented jobs. I'm unsure of the cause of the signal degredation.