As far back as 2007, Facebook's terms of service prohibited using one's profile for ad purposes (such as embedding affiliate widgets, for example): "You agree not to use the Service or the Site to upload, post, transmit, share or otherwise make available any unsolicited or unauthorized advertising."
The TOS have since been updated, but their current version has a similar language: "You will not use your personal profile for your own commercial gain (such as selling your status update to an advertiser)."
Would "liking" Walmart's profile in its Crowdsaver campaign qualify as "selling your status to advertiser" and could getting a deal on a product be interpreted as "commercial gain"? Tricky.
And it doesn't seem like the TOS is stopping a growing army of entrepreneurial individuals from mediating the relationship between people seeking online fame and people looking to make a buck. I easily found half a dozen services that are prepared to pay you for a range of Facebook feed-related activities, from posting status updates to "liking" stuff.
Here, someone who seems to be an affiliate is promoting one such service with an ad on Craigslist.
The service -- a Facebook app -- promises that "from the moment you connect to this app, you can start receiving money when you SHARE videos. Simply keep on sharing videos with your facebook friends, just as usual. The only difference: You get to receive money."
page on MyLikes says the service has 221,236 publishers (that is, Facebook or Twitter users) with an aggregate audience of 310,785,405, and has generate 43,023,415 clicks for its advertisers. The company has a write-up in the Crunchbase. Its Twitter account has over 31K followers. You can "Like" stuff on the go, too, using their Android and iOS apps. (The service is Twitter-centric, but it allows users to post their "likes" on Facebook even though it doesn't pay for any Facebook-originated clicks.)
PaidStatus offers access to "promotion-ready Facebook users". And at a $.85 CPM, it sounds like a good deal, too: "As at October 2010, direct exposure to 1,000 Facebook users works out at just 85 cents!"
VideoLikes specializes in promoting videos via "liking".