This is what their web site says:

Joining e-Rewards is FREE and by invitation only. Our Sponsors send invitations to their customers inviting them to join the program. If you've provided your e-mail address to one of our Sponsor companies, you could receive an invitation to join e-Rewards.

The list of partners is on their site. For me anyway compared to past years the surveys have slowed to a trickle and most of the time I don't qualify for the few I get so I end up with 25 or 50 cents each time. At $25 for the smallest airline reward it's hard to get there from here.

Good luck.