The reason I do not ship Draco/Ginny, Draco/Hermione, and Harry/Draco is because of the OOC-ness. The way they're usually written is complete with Punk!Ginny or Makeover!Hermione. And I believe that Harry and Draco hate each other too much to ever just leap into bed and screw each other senseless.
If it is well-written and true to canon then fine. But Draco has been awful to Hermione, calling her a Mudblood and such. And Draco hates the Weasley's, saying awful things about their financial situation to Ron's face. Yes, not to Ginny directly. But if it is well-written it can be truly great to read. I've just read one too many fics where Hermione is a blonde, and she is all of a sudden really hot and then Draco starts making passes, etc.
But I'll read H/D, D/G, and H/D if it's true to canon. I just have issues with Ginny-Sues and Hermione-Sues. And H/D seems to be the new thing on FF.Net. And it's usually written so badly that it's just not plausible.
That is all.