Take this with a grain of salt as this was posted as a comment on GreysAnatomyNews.com and has not been confirmed anywhere else, but apparently, Eric Dane [Mark] has been given the option to return next season for eleven seasons and Sara Ramirez [Callie] has not been approached. Plus, she's signed up to star in a movie that would shoot in Canada during December 2007, when Grey's would be shooting in Los Angeles. Here's the full comment, posted by Madison:

Our sources have confirmed that Eric Dane was given an eleven episode option next season which may or may not be extended for storyline purposes.

Sara Ramirez, however, has not received any offers from Shonda Rhimes and Company. Her agent Ray Moheet, confirmed via telephone, that there is a movie in Ramirez’s future. Quite telling is the fact that he confirmed the dates of the filming (which takes place in Canada) for late 2007 (Sept-Dec). If Ramirez had been asked to continue playing Calliope Torres on the hit show, she would be required to be on set in Los Angeles, California during those dates.