Your PC is only as secure as teh user. Not as secure as the stuff you have. Yeah UAC is a nice tool. It does help. But for people who know PC's and how to keep themself secure UAC is overkill.
To this day i still have yet to even get spyware on my PC. I have had no known virus in several years. I have always used the Admin accounts. I even have my wife on the admin accounts and she doesnt know much about PC's yet she is secure cause of the steps i have taken to secure the PC.
Using the right software for firewall/AV will always be better than using a Standard User account. I dont even have a firewall installed. Cause i took the steps to secure my network with my router so that the access doesnt get thru.
For a person who isnt all that knowledgeable i would agree. Yeah a standard user account is more times than not the way to go. But if you take the steps to protect yourself using a standard user account is just overkill. It wont really serve a purpose. Other than to be a annoyance when you want to do something.