Thanks. This is very useful, especially since the master/reader terminology is a bit unintuitive, to me at least. I kind of expected a writer to match up with a reader, and a slave to be a connection that wasn't a master. Silly me. :)

It's probably worth mentioning that $u->do and $u->select* functions are all running against LJ::get_cluster_master( $u ), since those functions may be familiar to people.