I am going to launch a membership site soon and will have a referral program (refer a friend, get x). Now, how should I structure the links so that I get the most for seo? Should I like to index with variables? e.g. site.com/?ref=28174 or a separate page, mod_rewritten which then forwards to the homepage e.g. site.com/join/28174 ---> redirects to homepage or this there another better structure?