this site pays extremely well but projects are few and far between. most of their projects involve food and food preparation and involve multi-day interactive boards, where you log in at your leisure and respond to a series of questions.
you can expect a screener about once every month or so, which can be lengthy and involve open ended questions. i probably have answered 30 screeners but have only been accepted into 2 studies. even so, i jump on every opportunity since the studies are fun and interesting and pay very well.
here is their link to sign up:
http://www.the-collaboratory.com/invite/