I'm boxing on a 17 inch macbook pro. I'm currently at 2gb of ram but have upgrades to 4gb coming in the mail tomorrow.

2 boxing is fine for PVE. Some might think PVP would be too slow. probably around 30 FPS on both clients. Higher if I drop the FPS on my background instances.

3 boxing is also just fine for PVE. Probably being a little bit low for PVP though I'm not sure. I'm sure it'd be fine for some people. Probably still hitting 25+ FPS on my main instance with 3boxin

havn't specifically 4 boxed, but 5 boxing was UBER slow. I could go around the world and do stuff but I was probably not going over 10 FPS. I'll update when I get my ram tomorrow.

Oh, I'm using ClonedKeys (http://code.google.com/p/clonedkeys/) and it's got active development thanks to Alphaquam.

I havn't figured out a good system for interfacing my mac with a PC yet, though I havn't spent a ton of time trying.