I do like Dawn for the Dawnyness (and I loved her in season 7), but just sometimes, especially in season 5 she could be just such an annoying pain! (But guess that's just like a typical lil sis, huh?). I think what most people's problem with her was subconsciously we all felt she was invading our memories too. Like we'd technically been with Buffy and everyone those four years and then suddenly Dawn is too- total cheat, hehe. Ya get me? Plus,I remember someone saying to me once that not many warmed to her because it was a bit of a family member exchange. Like Joss killed off Joyce and gave us Dawn instead and that made people a little iffy.
But yeah, Dawn herself I like. I guess it's just the concept that kinda annoyed me. But in season 7 she's great because this is the first season where she has actually grown up and is all making with the independency and personality-having...