I got a "Cables to Go" 4-port USB KVM switch. It's a nice-looking unit with rubber "ears" and a hefty feel, but the result is mixed. I read a lot of negative reviews of cheap KVM switches and figured out how much it would cost to buy cables separately, for units that didn't come with cables, and so decided to pay extra to get a a somewhat higher-end unit that came with decent cables.
Video switching seems to work great, and the video quality (contrast and detail) seems only slightly degraded. But far more irritating is the USB support. I'm using a Kensington Expert Mouse (my favorite trackball) and keyboard. The keyboard is sometimes not recognized at boot time on the PC, and the mouse works quite intermittently.
The other computer is a PC with Linux and Windows 2000 dual-boot. If I boot that machine with the keyboard plugged into the PC directly, and the mouse plugged into that, or the keyboard and mouse plugged in to separate USB ports, then I can always control GRUB to select whether to boot Linux or Windows.
In four out of five tries, though, if the keyboard is plugged into the KVM and the KVM, acting as a hub, is plugged into the PC, and I boot it, the keyboard is not recognized, and I can't control GRUB. So right away I have to start re-plugging things to even boot Linux.
And under both Windows and Linux, the mouse is recognized only intermittently. Sometimes after logging in Windows will _then_ decide it recognizes the mouse, and immediately ask you to reboot to use the new driver (except it isn't a new driver, it's been there for a long time, and worked flawlessly up until now -- except with the KVM box). And then you can't use the mouse to say "OK," and the dialog box that would let you do so comes up permanently stuck with no focus, so I can't use the keyboard to alt-tab to it, even though the keyboard works, and so I have to get creative just to get Windows to reboot the machine. Ugh.
When I'm controlling the Mac, the keyboard is properly recognized by the hub under every circumstance I could test; however, the mouse is also only occasionally recognized. For example, if I unplug it and replug it into a different USB port on the front of the KVM, sometimes it will magically start working... but only sometimes. As in "I tried it three times and it suddenly worked, then the next time I switched back it wouldn't work even though I moved the plug around seven or eight times."
Now I just happened to get Linux started up successfully on the PC, and this time I was able to use the keyboard to control GRUB, and Linux came up with the mouse working. I switched to the Mac; the mouse is working. I'm typing on the Mac. I decide I want to switch to Linux, so I do, and then the mouse won't work on Linux. It looks like the idea of switching off as the mood strkes me is just not going to work reliably.
Maybe this won't actually be a problem, because I can't record when the PC is running anyway; it makes too much noise. So, in typical use I might only want one of the two to actually be on at a given time. But when I have them on, I want them to work reliably! If I can't boot Linux without moving plugs around, what is the point? And If the KVM won't work reliably let me start up and use my Mac Mini and reliably act as a hub for the keyboard and mouse, I can't really use it -- the Mac Mini only has two USB ports, and I need one of them for the Snowball microphone.
And, finally, sometimes it won't even _switch_ reliably. I switch to Linux, and a couple of seconds later it switches back to the Mac, on its own. Or it won't let me switch away from the Mac.
So I have to decide if I"m going to struggle with it, or try to get tech support, or try to return it. USB ought to be well-understood by now; why don't these things just work?