This post on IMDB says that Kaley and Jim were VERY close during a recent taping.
Also on "Who's dating who", someone wrote "Kaley Cuoco is currently dating actor Jim Parsons" and I can't imagine why they'd make that up.
And in her official Bebo profile, it says she's in a relationship, and it's fairly current. (She last updated a couple weeks ago)
If this is true, I'll be very happy. Maybe they'll push for S/P to have more scenes? It's no wonder they have such great chemistry. <3