I have signed up with userinterviews.com for one month now, and have been "matched" to research studies many times. I've completed all the surveys I've received, so an enormous amount of data has been collected about me. But, I've received no offers to participate in the actual "official" studies, so I'm out the time it took to complete all those initial surveys, some of them very lengthy. The worst, is knowing that a lot of data about me, some sensitive, has been collected, and likely will be sold/shared. I deeply regret signing up.
If you have any information about userinterviews.com, please share in a comment below.