I run as an Admin at home.
Why? Because all my games need it.

The problem is that a lot of applications (or games) tend to put the configuration files in the same map as the executable in the program files folder.
When you run as a normal user, changing something in the program files folder is not allowed -> that's probably the main cause of all problems.

The recent games from EA: Simcity 4 and Command & Conquer: Generals are now using the My documents folder to store user only stuff in it, but those folders are getting to big in my opinion (186 MB) and you still need to login as an administrator.