I signed up for panda research (I assume that's what you are talking about) many many months ago and I still have 30 dollars pending. I feel like they are a waste of my time especially since they haven't credited me for the offers I did at least three months ago. I do have six dollars credited though although five of those is the money they gave me to sign up. You also can not cash out until you have 50 dollars doesn't seem like they are worth it. I have also heard they don't pay from other online searches I have done on them.
Don't know anything about nielson though.