To respond to a few folks:

MSE is more effectively hooked into file accesses than NOD or Avast etc., so it should load the system much less than the others. It also updates efficiently. Corporate AV is still not improving as much as you'd hope - there are some builds which work, but generally they are a complete pig. Macafee are doing good work with their DLP solution, though, so maybe that's where all their good devs have gone...

I always recommend MSE and chrome for home users with AdBlock plus, AdAware and NoScript - this will help protect you.

Also make sure you aren't running java unless you need it (If you are a java dev you may need the full environment, but otherwise get it off)

Windows 7 is now a pretty secure OS (and even XP with SP3 isn't bad - it generally is not the problem when your PC is exploited. It's the browser, flash and java)