I've used super expensive KVMs in server environments, and I've used Super Cheap ones at home. While I didn't feel like shelling out $800 for the high end one like where I used to work, I have three different types at home (haven't got around to sellgin the others).
One is an IO Gear USB Hub which I absolutely HATE. It works fairly decent mind you.....but I just don't like having to use a USB Keyboard (which yes, they suck). It's a 4 port with cables. THey're pretty inexpensive now....but the biggest problem I ran into using those is the shared USB Hub.
The second is an older KVM that was excellent. CYBEX 4 port.
The third is a Belkin 8 port OmniView KVM and I love it. It's got OSD, easy to use, and it's expandable.
One note: Buy.com and others have KVM kits for about $40-$60 usually that are 2 port with cables. In using the ones at home, I don't have any servers, and all of my 4 computers need a high resolution for my large monitor. So, I learned the hard way that cheap KVM Cables suck. Since I run at 1200X1080, I ended up going with both Belkin and Startech $30 cables, but @ 1200X1080 there's almost no discernable distortion (note: You do have to lower your Refresh rate to about 70 though)
Anyway. Just my .02.