Here's the scoop from Ausiello at TVGuide.com...

You mentioned a while back that George's mom was returning to Grey's Anatomy. Did the strike push that back? That's what I'm hearing. According to my Seattle Grace mole, Mama O'Malley's return — originally slated for November sweeps — was delayed until Episode 11, aka the show's final pre-strike episode. That probably explains why George had little to do during the just-wrapped two-parter. Why'd they move her out of sweeps? Well, per my spy, when it became clear that eppy 11 might be the final hour of Grey's we get in a long time, the script underwent "massive rewrites" to ramp up the drama and add several cliff-hangers — one of which involves George's old lady. "They're pretty big bombshells," says the source. "Basically, everyone's futures are left up in the air." Well, not everyone's. As I reported in this week's Ausiello Report vodcast, by the end of the episode there will be little doubt which direction the Mer/Derek/Rose triangle is headed in. [Basically, Derek will dump Meredith's "whiny ass" for Rose.]
Earlier this season, you teased that someone's getting divorced on Grey's Anatomy, and it's not who we'd expect. After reading your Bailey/narration spoiler, it has me thinking that it's her. I can neither confirm nor deny that Bailey will be getting a divorce this season on Grey's Anatomy.