Jessica, over at Online Marketing Blog has a great piece about earning money with social media. She looks at how to develop content specifically for social media networks. She lists some great ideas she picked up from PubCon 2008.
As Jessica points out, you have to be sure you're always operating within the rules of the particular social network you're looking to get traffic from. One thing you don't wanna do is get labeled a spammer and then get banned.
(pic via Manish Pandey)