I'd tend to agree with trimar7 on this one. I've been approached a few times by people I know trying to get me into their latest network marketing scheme. Over time it always ends the same way and all they end up doing is alienating the people around them.
I put links to some of my hubs and blog posts on social networking sites, but I never expect much from it. People who advert their networking businesses through these same sites tend to do so with more desperation. This makes me feel bad, especially when I need to turn them down... I end up just removing them from my contacts.