Every patch day I can recall, the server I played on (Illidan) has been unstable or unplayable for hours afterward. Is it 100% of patch days? No, but it is damn near close.
There's your problem. I played on Illidan from vanilla to early WoTLK release. Transferred off after I got sick and tired of +800 queues and the unbearable lag.
Went to KJ and everything was much better. In fact, our server only experienced minor loot lag issues on 3.3.5 release. It was fine the next day. I also play on Tich and Blackrock after 3.3.5 was released. Pretty sure it was no where as bad as Illidan during any times when a new patch was released.