For work I run VMs that contain toolkits for development on different clients. I used to run these locally. My limits for working on more than one client was limited by memory. At about 8 gigs of memory, you might be able to run two smaller VMs, but it got slow, so I never bothered.
Lately, I connect remotely to hosted toolkits. I can work on two clients now given my bandwidth. It's not perfect, I could use more, but it works. I could do three if I had a local toolkit and two remote toolkits (I do this for internal company work on side projects). Same screen paint issues regardless if remotely connected to one verses the other. Now my local memory is free on my machine, but I use it for browsers, a shell and twitter mostly.
One last thought, if you want to know how your application performs over a site to site VPN via remote desktop with average bandwidth, contact me for some test. I really hate how Firefox repaints when you refocus to it. I really hate how Eclipse flys out all those bubbles for suggestions when you hover over something.