You are all going to rip me for this, but personally I don't think Sara is very attractive, however, the writers have made her so in the sense that Greg & David have had crushes on her, and she also had the relationship with Hank, therefore it isn't like she is some bottom of the barrel broad that Grissom is going after.
Jorja has a unique face. It's why she was a model - good bone structure, and a different look. She's not everyones' idea of attractive. I think you also have to kind of consider that David and Greg are nerds, and here comes a new nerdy girl in the lab.
As for Hank, well, he was a jerk anyway. lol.
I don't know if I get the last comment, though - are you saying that she
is bottom-of-the-barrel, or that TPTB are trying to make it seem that way
after the fact?
ETA
I also don't picture Grissom as the kind of guy to whom looks are the only priority. I mean, he could have had Lady Heather (who is, to most people, much sexier than Sara), he could've had Teri Miller (ibid) and he let them go. Not necessarily on purpose, but whenever he's done something equally stupid with Sara, he's tried to keep her the next episode or at the end of the same episode. Sending the plant, telling her she's beautiful...
I think that he's allowed things to sour between himself and Teri or Heather in a way he wouldn't with Sara. And some say it's because Sara was more persistent, but I disagree. He got closer to Teri or Heather date-wise than he did with Sara, and
then he walked away.
By the time he got to that place with Sara, he was in the relationship, not just trying things out.
I also want to say this about Jorja's looks: seeing her at award shows lets me know that Sara is drabbed-down and dressed-down. I do a street test with most "ugly on TV" women. If I could picture them walking down an ordinary street, would they be more attractive than average? In Jorja's case, I would say yes. Marg has a va-va-voom effect that they don't let Sara have on the show, and that could be a big part of it.