Pay with a tweet...

Found an offer for a free ebook today. Of course, anytime something is offered for free on the internet there's usually a catch. The catch in this instance was simply that I agree to send a single tweet about the fact that I downloaded the story. Not that I had read it, not that I liked it, not that it was a good story or anything like that. Merely that I had downloaded it for the price of a tweet.
There is a website with the imaginative moniker of www.paywithatweet.com and all you have to do is place a button on your website linking to your book - or any other item you want to sell, including music, movie trailers, or what-have-you - and it's all free. You tell people about the offer and provide the link, when they arrive they click the paywithatweet button and then send the tweet and download the item. Simple as that.
There is also the option to pay with a Facebook post, the idea in both cases being to use the extended "family" of all the people who download the item as word-of-mouth advertisement. I haven't tried it myself - that is, I haven't offered to sell anything for a tweet. But I will, and I will get back to you about my experience with it.