Zap2It at Comic Con. If you've seen the show (and are obsessed with it like we are), you'll figure it's Penny's mom, which Mullally figures to be as well. Mullally will fit right in. Look for more character development this year for those who aren't Dave and Alex. We'll possibly get to know if Jane has a job! The idea of season two will be less serial (which it really wasn't that serial if shown in the real order).
PS--Happy Endings is the best show you're not watching. It has taken the place of our dearly departed golden child Better Off Ted. It's got the same humor at BoT and the same character interactions as It's Always Sunny in Philadelphia.