Speeding up StackExchange
blog.stackexchange.com
blog.stackexchange.com
It sounds like they are still using a different database per site, as opposed to one database and scoping data by an account_id. I wonder what the performance gain is over the complexity it adds.
I remember this is the same way that FogBugz was setup too and they ran into issue when they had so many small databases instead of one large one.