This seems like a great way to browse the web and keep your box clean from all the bad stuff out there.    I'm running my browser in a sandbox right now, and I don't notice any performance hits, which is cool!  It's one extra layer of clicking if you want to really save something to your real computer, but that's not so bad.
For cruising those nefarious sites ,it looks like it's going to be ideal to keep your machine nice and tidy. 
 
  I  just ran Spybot, AdAware and Asquared and got my computer as clean as I could.  Now I'm going to just run my browser in a sandbox for the next week or two and see what it picks up when I run the next scans....fun, fun.  For admin that surf the web from their main box, this might be a must have!

http://www.sandboxie.com/