1. When people who are not on a jury decide for themselves whether they believe in an individual's guilt or innocence, that is not the same as violating the "innocent until proven guilty" principle. You are innocent until proven guilty before the law -- time wasters with an internet connection across America can decide whatever they want, whenever they want.
2. Pretty white girls probably do get a disproportionate share of media time when it comes to being accused of violent crimes, but it really doesn't do them any good. For every Amanda Knox who has the public outraged on her behalf, there's a Casey Anthony who will probably have to go into hiding if she is exonerated. Being a media sensation is a double-edged sword.