ok, one down.
Leave Mail Sheild off though - any file that hits the system will still be scanned by the file system shield and possibly the behavior shield. The Network shiled seems to prevent threats nicely (warns if I visit a site that has questionable objects) - this might be a bit heavy, so the user has to decide the risk - I normally just leave the site.
Note: I only install File, Network, Behavior, and Script shields when I install Avast 'be free'. The other shields (Mail, IM, P2P, and Web) are, in my opinion, redundant. I also disable the cloud services - a twice daily virus def update seems sufficient (I don't need constant update checks). I definitely do like the sandbox.
It's just my personal choice for Avast (or any malware product).