Running as non-admin is theoretically good, but in practice it's such a pain and so many things don't work (esp. games) that I don't. If you're prepared for a LOT of tinkering with MakeMeAdmin etc., you can get a reasonably smooth non-admin experience, but it's a PITA.
Mac, I usually agree with 99% of your posts, but in this case it's the 1%!
I find it a non-issue to simply "run as" administrator (win XP), either to install or to run apps (games included). OK, I have to type the admin password, but I can type this so fast it really isn't a problem!
Compare this to the hassle when my wife downloaded a "screensaver" trojan before I instigated the no-admin policy!
It also means that the boys have to ASK to run some games that require an admin password - a handy bit of extra parental control!
SD