I'd expect at most a few days might be compensated, similar to how Blizzard compensated people who attempted to log in during the first few days of Warlords of Draenor when their servers all collectively crapped themselves from the sudden arrival of almost eleven million people after years of just under six million.

All in all? This is annoying, and people have a right to complain. Doesn't mean they need to have fraggin' panic attacks about it and act as though it's the end of the world. If anything, I'm glad it happened now and not on the main release date; hopefully, they'll have a fix out tomorrow.