Do what I do when shopping around... only read the negative reviews... there are ALWAYS some. I did this while shopping for a good KVM switch and learnt such a lot.
Most negative reviews were from people who did not understand some aspects of KVM switches, such as why they may only support certain resolutions (they need to emulate aspects of the display) active keyboard and mouse emulation (since when the switch is not active on one computer, that computer must still think the keyboard/mouse/screen is plugged in).
So what I did was learn from the negative reviews and choose the product with the least amount of negative reviews that related to me.
I ended up getting "IOGEAR GCS932U MiniView Micro DVI-D 2 Port KVM with Audio and Cables" and it worked perfectly for my setup, which is a good thing since my setup was what gave a lot of other KVMs problems.
My setup:
Logitech Mouse
Mac Aluminium Keyboard
DELL 24" Ultrasharp 1920x1200 display
Shared between a PC and a Macbook Pro (Both with DVI)
And I'm very happy with my product, thanks to reading countless horror stories with other products.