You earn points on Crowdtap based on your answers to surveys & polls, as well as your participation in the discussions that are offered to you. Once you rack up so many points, you can cash them out for select gift cards, Crowdtap merch, or donate to charity. You used to be able to receive a check for your points, but recently Crowdtap has changed their rewards system. It is still a decent system as I just cashed out for the first time since I have been a member (about 8 months now), and I got $60 in Amazon credit. and still have some remaining points.
The bottom line is if you have a bit of spare time and have Internet access, sign up for Crowdtap. They don't spam you with e-mail or sell your information. If you don't log in or you want to cancel your account, it is easy to do so as well. I can't think of anything that I don't like about Crowdtap, and there are a growing agency with new companies joining them for campaigns every day.