I got a used MacBook running Snow Leopard. I installed EE2 and Xcode 4.2 for Snow Leopard.
The CPU usage of EE2 is very high. Even when minimized it had a constant 20% CPU in the activity monitor. Opened it had 50% doing nothing. The system is not the newest, but it's 2 GHz Core 2 Duo and the other applications are running smooth.

+1

EE Editor can do background processing of project elements/worlds, etc.