If they where would have been annouced and poepel wouldnt still be in game obiously.
It's almost 3am on Sunday in the US. I doubt they're going to announce every little maintenence check or update. And just because they're doing something with the servers doesn't mean that everyone would suddenly crash out of their current games, altough that does seem to be what happened to people at the match loading screen at least.
As for logging in, it was fine for me. I saw those 2 games hosted by MABManZ as well on the custom games list, but I didn't try to join anything. It's weird that there are so many games this late. I'm not sure if it's a bug, if they're doing something to the servers or what, but I'll hold off on playing for now until we know what's going on.