Im using 2 pc's, and 3 monitors.
My first pc runs 3 wow clients and its a Dell XPS 630I with 2 monitors. It has a Intel(R) Core(TM) 2 Quad CPU, 1GB NVIDIA GeForce GTX 280 graphic card, and 8GB ram.
My second pc runs 2 wow clients and its a Dell Dimension 9200. It has a Intel(R) Core(TM) 2 CPU, NVIDIA GeForce 7900 GS graphic card, and 4GB ram.
Im using Keyclone to control all chars, and Synergy allows me to use same keyboard and mouse on all screens (both pc's).