I run multiplicity and keyclone on my 5 box. I used to have synergy and multibox but a couple of my pc's kept having very bizarre crashes (although connecting was fine) which started to get infuriating.

Since I made the change it's been rock solid and the crashing has stopped. Keyclone is $10 per license but I think its worth it (plus it also has the functionality of Autohotkeys which is a bonus).

See link below:

http://solidice.com/keyclone/