They're doing some sort of maintenance, but were a little late in shutting down Battle.net as they noted to you on the left hand side before signing into Battle.net.
With that said, lots of people were encountering problems with StarCraft 2 freezing in the Loading stage when you open up the game; and this is normal.
What some people did was -- is they wasted time in re-installing the game / client which did absolutely nothing. So I'm here to let you all know that Battle.net is down along with the Battle.net website and to not re-install
the game as I said earlier will do absolutely nothing/fix anything.
Al though what you can do is if you unplug your internet and open up StarCraft you should be able to play offline and do Campaign/Watch replays.
Just warning you guys so you don't waste your time with anything else with trying to fix this problem as it should be fix sometime this afternoon/evening. <3
Sources of people having this identical problem:
Battle.net down: http://battle.net/
Edited by Sawyer, 20 October 2010 - 01:09 PM.