Forget all of those rumors indicating that TR Knight will be leaving Grey's Anatomy next season! Here's Michael Ausiello from TVGuide.com:

I read that T.R. Knight is leaving Grey's Anatomy. Noooooo! Please tell me this isn't true.

(Major spoiler alert) T.R. Knight will be back next season.
I have a sneaking suspicion (spoiler alert) that the McSlutty girl who hit on Derek at the bar is Meredith's half sister.

You're not the only one.