At one place, I was faced with a C# solution which when XML documentation was turned on, the compilation time increased from 45 seconds to over 8 minutes. This slowdown was unacceptable, however some digging revealed an excellent suggestion by Eric Woodruff at http://social.msdn.microsoft.com/Forums/en-US/devdocs/thread/9bbad4cc-e229-49da-a6f7-3cdf470ac53a/ where he suggested "just suppress the warning by entering it's number (1591 for C#) in the Suppress Warnings field on the Build tab of the project properties".

I followed Eric's suggestion and the compilation time went back down to 45 seconds. Now that CS1591 is suppressed how was missing documentation to be found? All that was necessary was to run StyleCop!