My site is showing up for my major keyword phrases in Yahoo and MSN but I'm nowhere to be found in Google. Why does Google hate me? (Or alternatively, my site was doing well on Google but its rankings have suddenly plummeted. Am I penalized?)
That is simply because you didn't follow Google's Webmaster Guidelines. You might be also penalised for some reason, and that reasons would might be the stuffs that you've done to your website.