Microsoft has recently released a least-priviliged user account (LUA) whitepaper that's a great read if you're contemplating running as LUA (which you should be) or about to.  As any follower of my blog knows, I have been successfully running as a LUA for about 3 years now and absolutely loving it.  In that timeframe I have had ZERO viruses and ZERO mal-/ad-/spy-ware.  I've been a long-time supporter of Aaron Margosis' MakeMeAdmin, having customized it so that I have an admin console for VS 2003 and one for VS 2005.

At any rate, read it - it's good for you.