Yeah, the only ones I could stand were Vi and the Chinese girl. Amanda was just okay, though she had her annoying moments. The rest were awful, especially Kennedy (but I admit, although I still would have hated her, she wouldn't have been QUITE as bad if she hadn't gotten into that absolutely atrocious "relationship" with Willow), Rona, and Annabelle (it wasn't the character, though. It was the British accent. I don't know if it was fake or not, but either way, it sounded so ridiculous and grating.)
I think the main problem with them was that, after a couple of episodes, they completely took over the show. Usually, the "annoying" characters weren't like that. In season 5, when Dawn first joined and had the "obnoxious, whiny teenager" role, the show still centered around the core Scoobies and everyone had their own little plot to keep us distracted from Dawn. Even in season 6, when Buffy had her occasional annoying moments, the other characters were there to make up for it. But in season 7, it was all about the Potentials. I know, it's probably because there were just so many of them, but we barely got to see any of the characters we had grown to know and love. Instead, we got a bunch of whiny teenage girls that were way worse than season 5 Dawn not only as a group, but, in most cases, individually. If there had been more character subplots, I know it would have been much better.