With memcached it is important that all servers have the same options, 
otherwise a metadata cache entry by server1 will not be read by server2 and 
they'll each have to perform their optimizations independently.

John suggests printing it in the log, though that might get a little annoying 
because I think we might print it a lot due to custom options in .htaccess and 
directory scopes.

It might be good to print it in /mod_pagespeed_statistics, maybe including the 
last 10 signatures we found and the scopes that caused us to find them.