Casey will not go as far as Taylor Hicks did because he is offbeat and quirky, which will divide voters (a love him/hate him thing is going to happen, I think). Hicks was cute and cuddly (relatively speaking) and enveloped the audience, whereas Casey likes to challenge people (which is a good characteristic in general IMHO, but will not pull in votes).
I think people might have seen Thia is too cool/sombre...to the point of coldness. But in the results show when she cried about someone else being eliminated...I still can see the tears coming down her face...this may have warmed the audience up to her. Thia needs to stick to some upbeat pop songs for a few weeks...dance around, have fun, joke a bit with Ryan and the judges - and America could really warm up to her.