I think I've been 700 something on Illidan (That's 1/4 of the server's capacity in front of me in line; overpop much?). About 260 is the highest I've been on Blackhand.
When they lowered the server capacity on Illidan(less people could be on the server at once)the queue was crazy. Basically they replaced the horrible lag with a horrible queue that was at times 2+ hours long, and even then the server was laggy. I remember quitting WoW for a month or so because of it.