It's a good start to a nice little story; I can see at least one chapter more (where they admit their feelings to each other) and perhaps one more after that as they deal with the fallout and reactions when they go public with their relationship. It does not -have- to have Weasley-bashing, or at least bashing of all the usual Weasleys (I think Ron is inevitable, but Ginny is not, tnough Mrs. Weasley might well be), but I can't see it not having some. Beyond that, the reactions of the various Slytherins would be amusing as well as any others who were hoping to "snag", and snog, Harry as well as any who might be interested in Hermione after seeing her at the Yule Ball.
Author's response
At this point, I'm thinking it'll be three chapters total. Then again, I initially said Yule Ball Debauchery was just going to be a one shot, and that one will probably wind up at around 7 or 8 chapters when I finish it 15 years from now. So, perhaps I shouldn't try and predict the length of this fic.
If any Weasley will come across badly in this story, it'll probably be Ron. I think I'll have to address his reaction to this, one way or the other. Ginny will probably get nothing more than a passing mention. Since I try to sort of blend my stories into the canon, Mrs. Weasley won't be making a physical appearance unless I stretch this out to the end of the year, when she came to Hogwarts to support Harry during the Third Task. However, there's an incident from canon I'll be mentioning in Chapter 2 that might bring her reaction to "Harmony" into this story, even if she won't actually be at Hogwarts.
Your comments about seeing the reactions of the Slytherins, as well as others who may be interested in Harry or Hermione, have given me some ideas that may well be incorporated. So feel free to pat yourself on the back.