I tried running as power User for a long time, but eventually got tired of being told this or that didn't have permission or access. Now I use a router with a firewall, strong passwords, Zonelarm Pro, Spyblocker and good antivirus software. If someone comes through all that, what the hell - I just don't have any military secrets on my rig.
Yes, it is safest to not run as Admin. The script kiddies are looking from fresh meat all the time.