I've got a few ideas, such as front-loading the site with content and preference data by using differnt API's, such as Flickr's API, Youtube's, del.icio.us, Last.fm's. This way when you showup, lots of your preferences and rating "work" comes along with you. Additionally, the preference dataset is jumpstarted.

What you would tell your little sister about the site is "find more things you like, and if you're good at finding new content, be recognized for it."