Ah, I've always loved that Britney compliation
But to to be fair, as others have stated, she was dancing a lot, and that was never intended to be heard. Plus I doubt most people ever took her very seriously as a singer, as opposed to a performer.
Anyway, this Susan Boyle explosion has been on my nerves since it began, and I'm glad to see I'm not alone! Yes, it was an inspiring performance, and I absolutely applaud her for her courage. People have every right to be moved by what she did, I don't have a problem with that. Her singing was by no means bad at all, but frankly, it's really only basically good. Everytime I see comments about how "amazing" she is, and the "best voice ever," I have to wonder if the only singing those people have ever heard is the latest top 40 hit on the radio. She has a very generic sound that most talented high school/college performers could replicate. She's very out of tune and has little sustaining power. I'm not saying it to be mean, it's just that technically she's not that good at all, and the vast majority of professional singers are considerably better.
Again, I'm perfectly happy for her and what she's achieved. If you enjoy listening to her sing, that's fine! It's just incredibly frustrating as a classically trained singer with many friends who do music professionally to be bombarbed by "isn't she the most amazing incredible vocalist you've ever heard!" Well no, I hear better when people are marking and half assing their way through opera rehearsal.
/end rant
Oh, and on the whole physical appearance issue, I find a rather strange disconnect between vocal and instrumental music. If an average looking person got up there and gave a stunning performance of a cello concerto for example, no one would be talking about "omg, that ugly person can play the cello so well!" Why is it so different when the instrument just happens to be the voice?