I signed up for these iPhone apps in the last month to start a baby savings fund since we're TTC, and I have to say that I've been pretty impressed.
Basically, they offer opportunities to do quick store inventories, taste tests, surveys, etc. Payouts are usually in the $3-$15 dollar range per "gig" but I've seen some as high as $40. Upon completion cash is deposited to a PayPal account.
So far, I've only been signing up for jobs that are at stores I'm already in, or I drive by on my way to/from work or when I'm running other errands. So far, in the last month I've made about $50, but I could see if you have the time and dedication (and are in a bigger city*) making a lot more. (*I will say that I've been surprised how many rural opportunities there are too, mostly at Walmart.) Today, I did a Field Agent job that had me buy a certain coffee at a particular coffee shop. They reimbursed the cost of the coffee, plus paid an additional $9.
So, if you're looking to make a few extra dollars, I would highly recommend.
HeartlandHustle | Personal Finance and Betterment Blog
Re: PSA: Field Agent & Gig Walk