This video more than anything got me interested in socialcam (of which I had never heard of before), so I did a little reading and decided to sign up for updates to the product. After I signed up the page refreshed and informed me I was ranked last (4000 and something) on their list because I hadn't gotten anyone else to sign up yet. Instantly my competitive juices started flowing and I wanted to get higher up on the list.
It just struck me as a really original interesting way to encourage sign ups (presumably for eventual beta testers).
(also you can help my ranking if you click here: http://socialcam.com/?referred_by=BEA3CDhw )