Vaksel- Awesome point. You inspired me to write a post on exactly what you're talking about: http://marketingstartups.com/2008/12/15/10-tips-on-attacking...

Tell me about it, my social site relies on heavy user participation (in fact requires it) to be useful to other users. And unlike Digg, my content is worthless 24 hours later meaning I can't 'seed' the site with my own content effectively.