I have won quite a bit - I used to enter contests online everyday through
www.online-sweepstakes.com. I have won $10,000 in a Kraft Foods contest and I won a $1500 Panasonic television in a Cablevision contest. I have won numerous smaller prizes as well. You have to make a pretty big commitment to entering, enter a lot during odd hours (i.e. middle of the night), but you can definitely be a winner.
While it sounds great, you can probably make more money if you spent the time that I spent entering contests at work for a salary. But, it is a lot of fun when you win something. I won the $10,000 after sweeping for 9 months.