Well, personally, I always thought Quentin and Julia were really hot together in their scenes, especially when she's bossing him around during the Grand Douglas period. I just love Connie's novel in which she envisions them, very realistically, as a couple. They both have a certain world-weariness and are beyond the notion of romantic illusions in a way that makes them suit one another (but then, in the episodes currently running on Sci Fi, Quentin displays some phenomenally ga-ga behavior around Daphne).
The other somewhat more negative reason to see Quentin and Julia together is imagining Barnabas' facial expression upon his discovery of the situation. Knowing his usual degree of self-involvement, it would probably be when they've gone to visit him at the Old House to let him know that they're setting a date.
Oooh, just imagining the scene is sending off vibrations!
G.