Pocket Fives has a review of the Stars VIP Program. Currently the site is down.
I believe if you make SuperNova Elite, it's equal to 40% rakeback.
If you make SuperNova status, it's equal to 28% rackback.
You can achieve SuperNova status playing 50NL. It depends on the number of tables and hours played. Poker Stars has a VIP calculator on their site.