They take the servers down for maintinence on the databases each day at the same time which for me is 7:05pm(I'm US Pacific Time). This is also the time when they start running the matches for the tournaments. Generally the site is down for roughly 2 hours I'd say. I've seen it down for longer, but I'm pretty sure thats been in conjunction with server upgrades, or rolling out updated code. They may also do a big database defrag and purge a lot of the crap brutes that aren't played anymore every so often. The site has been up for me everyday I've checked to play though.

Oh, and gratz on impact Goz. Now he's a contender...