^ I understand what you guys are saying about the lack of screentime, but, as episode arcs go, I think it has less to do with any antipathy on the part of the writers toward Greg himself and more to do with the nature of the show. There just aren't that many character arcs, in general.
It feels like the only real character arc Warrick has had after the first few S1 episodes was his departure arc. (Then again, I've always felt that Warrick was the least used character on CSI, especially in the past few seasons. I've always felt like he's the character that they've most dropped the ball on, as it wasn't until Dourdan was leaving the show that they really did anything with the character. Ditto for Doc Robbins, even though he's not a CSI.)
Sara's had the DUI and the Living/Dead Doll-departure-and-departure-again arcs, Griss had the oterosclerosis (hope I spelled that right), Paul Millander and GSR (and the whole honey bee arc that he was supposed to get for S8 before the writers' strike) and Nick had Kristy, Grave Danger and Stalker. Brass had Ellie, Bullet Runs Through It and the shooting in Way To Go. I guess what defines an arc or personal storyline is subjective, but I really feel like Catherine is the only character who's really had more personal storylines than the rest of the main characters.
As much as I wish it weren't the case (at least not as much), the show is built a lot more on the drama of individual cases than it is on drama for the main characters.