The problem with Ms. Boyle is not her looks its her stage presence - something that the show was banking on. TV shows milk this sort of thing. Bear in mind that she was not an unknown entity - Andrew Muir (a contestant from last year) knows her - they had done charity shows together.

As for her being off-key - I would say it was more an issue of out of range. The lowest note disappears. Even great singers have sounded strained (listen to Marvin Gaye sing Heard it on the Grapevine - the song was recorded out of his range on purpose)

Bottom line is - she can sing better than the average audience member and better than many a young popsie with the big record deals. With a little coaching she could do quite well.