UAC should not be turned off by computer users. It does actually protect a system against unauthorized access in some cases, and it really makes a user think about what changes they're making to the system.
Windows 7's version of UAC is far superior to Windows Vista's version, requiring prompts for less things that don't need it, or requiring it for things that could potentially damage the system even more.
UAC makes even more sense when you use your Windows PC the way it is meant to be used. That is, your primary account should NEVER be an Administrator account. You should set up your personal PC accordingly:
Your Account: User Account
Administrator's Account: Not the built in Admin account, but an account with Admin rights
The reason for this is when you go to use the system, for 90% of most tasks, you'll never need admin rights. When you do however, it prompts you for the username and password for the administrator account on your PC. This is just like using root on a linux system, since most user accounts aren't actually root.
This is also how a Windows domain (when properly set up) runs things. Users cannot change things on the machine unless they have the local admin account access, or the domain account access.
Those of you still using your PCs otherwise, thanks for the viruses and malware. Some people just never learn.