In the slides from Scott Guthrie's 'ASP.NET Tips and Tricks' TechEd Presentation, I ran across this gem.  You can turn off debugging server-wide by adding the following to <system.web> section in the server's machine.config file (typically located in C:\windows\Microsoft.NET\Framework\v<version>\Config):

       <deployment retail="true"/>

This is a great backup in case developers forget to turn it off in the application using <compilation debug="false"/>.  Scott also mentions a few of the negative results of forgetting this little setting:

• Slower performance due to debug code
• App uses much more memory
• Client-side scripts are not cached