I've been with them pretty much since they started in 2006 and have earned $1500. It probably would have been more, but for the first year I didn't really "get" it.
I've never purchased anything I would not have gone out to a store to buy anyway (I don't do the free trial stuff, like freecreditreports, etc). Daily surveys, freebies and cashback shopping, and a few clubs like Columbia House DVD.
It has gone towards my last wdw trip and some towards my next one, and also a few Home Depot gift cards that I used to paint all my rooms and get new window treatments. After next wdw trip I'll be saving them towards Home Depot again for a new fridge.
I highly recommend joining their forum and reading the stickies. There are certain things you should do, like cookie settings on your computer, making sure you use the same email address for daily surveys, etc. Sounds daunting, but once you get the swing of it, just becomes a normal part of the day. I have my coffee, try for some surveys, if there aren't any I try back later in the day instead of watching tv, or listening to it in the background!