I'm running on Windows 7 and I leave UAC on and my account isn't a true admin account. So when I bump into UAC, I have to enter the admin password to continue. Even under Vista I kept it on. I've heard a number of developers say it gets in the way, but I've yet to see that. Under Vista it was a bigger issue as several areas were a little too restrictive.
The question I always bring up when developers say UAC gets in the way is "What are you doing that you keep running into it?". If you are attempting to manipulate files in system folders (Windows, Program Files, IIS sites), you're doing something wrong. IIS websites can exist outside of C:\inetpub. SQL Server user databases can exist outside of Program Files. The only time you should regularly see the UAC prompt is application installs and updates. If you're seeing it more often you're likely working against the system rather than with it.