Maybe no one cares...  but I went through my entire project and here are the files that had what appears to be a potential timing issue bug (search for DataCache.GetCache).  The interesting thing is out of 27 files, only these 8 followed this pattern.  The rest followed the pattern I suggested.

Domain.vb
Configuration.vb
XMLLoggingProvider.vb
RewriterConfiguration.vb
ClientAPI.vb
UserOnlineController.vb
Localization.vb
SiteLogController.vb

After putting the changes on my site, the number of exceptions I ran into significantly diminished.

Without digging deeper into how the Cache expires, I can't say for sure this is the root issue.  That said, coding practices do say that you shouldn't return something you haven't verified to be null if the callers are not expecting null.  I also suspect the call would be faster allocating on object on the heap and assigning it once, rather then making another stack call to the cache function, though I'd have to verify that through ILSAM.

On my server, the random null reference exceptions I was getting for various functions all went away after making these changes.  The only exception I'm getting now is intermitent Thread Abort exceptions on the scheduler threads and a couple exceptions for the Forum module that I'd still trying to track down.

If you want details of the changes I made, I can either post or send a diff.

James