I was invited to join this panel through another survey, but anyone can sign up. You need the ability to download apps through itunes to do it, e.g. I have it on my iphone. I don't know if there is an android app for it but it's worth a look.
Once you sign up, have the app, and do your profiles you get invited to numerous surveys a week (I had 8 today). The cash out is £10 Paypal, which doesn't sound like much but it could take a while to get there.
The surveys are very quick, and are more like polls TBH. The most questions I have ever had is 5. They give £0.03 for each time you answer a one question poll. I got £0.16 fo the 5 question one.
I have been very impressed with how easy it is to use. I get notification in the form of a message to my phone when there is a new survey so I never miss out. There are no pending rewards, it is instant credits to your account.
I will try and keep those interested up to date when I get to the stage of requesting a payout, but in the mean time I recommend it to anyone who has the hardware to get it.