I had Memcache running for quite awhile on a large forum. I installed vBGallery things run fine for 8 - 10 hours, but then the entire site breaks including the admincp. All blank pages are returned for everything.
I've set it back to filecache and things work well, but it's important for a site of this size to be switched back to Memcache.
This did not occur before vBGallery which is why I think it is the cause of the problem.