I don't really get into all the ballet dancers and stuff, i find i only have time to do the dancing itself. But on those occasions when i do go to the ballet, I love it!!! So you can enjoy the ballet without knowing the dancers.
I can't really watch anything with dancers I know except the videos of our own performances. In these cases, like Doris said, i focus more on the one dancer and watch their performance rather than the general choreography.