Synergy does a lot more than a pKVM (for most people, as most people use it) even a super fancy one... as much as the Copy-Paste can be a pain in the pooper it still allows me to copy and paste _between_ the machines... And, of course, with Synergy I can have a single IO setup and see what it on my Windows box, right next to my Mac, and - say, be gaming on Windows and watching WANShow on the mac, and easily swing my mouse over to poke at twitch comments without actually losing sight of the windows desktop... Sure, it's a "Physical Screen Palaver" with more monitors than the KVM, but the operational functionality is very different...
-Dx