Jakob Nielsen's blog, Alertbox, is the Web's most concerted effort going on designing sites for usability. His latest post identifies the risks of outsourcing content to social media. His advice: Keep the best to yourself and don't share too much with social networking sites.

"You might be handing them the keys to your kingdom," he writes.

It's a bit counterintuitive, given the arguments on spreading content widely and benefiting from the traffic that tracks back. But Nielsen argues that social networking sites stand to do the same as search engines --- take the content and reduce the value of the originating sites.

Nielsen suggests holding specialized content back and furnishing only broadly-based content to social networks.