Everyone is into social networking. Its become the new buzz word in optimization. Just say social networking and it must be great for optimization. I honestly don't think most people know what they are talking about. They heard something and they are repeating what they heard. Like that bad movie that someone heard it was the best. The buzz came from the source.
My take don't put your content on any website that sells your keywords to other companies, don't put your content on sites that will not link back to your website.
Social networking is great to promote yourself if you have a following. Just like club or party promotion you need the following. Stop letting sites swipe your leads because they made you think its best for you.
Are you really that foolish?