Now you can add docstoc to a the list of document sharing sites where they don't have outbound links. I understand you've gotta control spam but do these people really think people are going to submit content just for a pat on the back.
You've got to have a relationship to make it work. Right now, it's one sided if you can't link to your website.
It looks like the document sharing sites have ran their course for seo.
I guess I can see why though, after checking out a lot of the niche stuff it's all just one big affiliate advertisement. This is why you gotta get in quick before someone else screws everything up.