If you value your sanity then don't expect the servers 100% up on launch day. Too many people hitting the login button killing the servers. Wait a for days.
Uh huh. That's the exact response I'd expect from someone who's planning on playing Day 1 himself, but trying to convince others not to so he can have error-free servers.
In all honesty though, you're probably right. Despite how big Blizzard is, they've always seemed to have a history with problem-riddled launch/patch days. Still though, I'll be one of the ones hammering the server when I get home from work that morning as that'll be the beginning of my weekend.