I use it to fund the in-app purchases for some games I play. For SuperCell games, I won't give them a dime of my real money, but I'll definitely use Google's.
Yah, why not? I had $15 to just answer questions. If you're smart just answer them with whatever and the longer you make the survey the more you'll make.
Anecdotally, I've noticed if you choose a "wrong" answer on some questions, it'll stop the survey and just pay you whatever rate per question answered.
It seems the first question is usually a litmus test to see if you're answering reasonably truthfully or not, such as "Which of these did you most recently visit?" with some answers being bogus names or businesses not located around you, and one correct answer based on location data Google already has.