It’s a hard line to draw, the one where someone is spamming your site with submissions, or just honest to goodness trying to get their voice out there. Although we do allow anyone to post a link to anywhere (within reason) else on the web, we are a "social" site, and I think that’s where it’s easiest to tell between those who are just in it for themselves, and those that are trying to give as much as they receive.
Eliot sums up our stance on mass submissions in this article from WAXY.ORG