There are many survey sites out there, and some of them are scams. Some can be beneficial, however. Delta Airlines partners with a site called e-rewards. Since Delta is a partner, those signing up and filling out one survey within 2 months can get 250 free Delta SkyMiles.
I tried out the site and filled out a survey within a day or two. The 250 SkyMiles showed up in my account almost immediately. Those who fill out more surveys can get e-rewards that are measured in dollars. These are not dollars that you actually get, but they are "dollars" that can earn free merchandise or travel rewards. The lowest amount that will earn a Delta award is $25, and I earned it in a little over a month. 500 SkyMiles can be had for $25, and I again got this in my account within minutes of requesting it. There is no progressive earning system with Delta, so it's just as well if you cash in the reward immediately after getting it.
A few hotel chains also have rewards available. These include Carlson, Hilton and La Quinta. The partners are subject to change at a moment's notice, but they are on board at this point. The rewards with these hotels will earn points in loyalty programs. For example, $25 in e-rewards will get you 1,000 Hilton Honors points. $100 will get $7,000, so it may be worth it to save up in that instance.
Most of the surveys can be done in about 5-10 minutes. Even if you don't qualify, e-rewards will usually give around $0.25 or $0.50 to try. It would be possible for someone qualifying for most of the surveys to easily get close to the $25 per month. This is just one more way to get miles for nothing but your time.
Please note that I do not earn anything by promoting this site. It is not a scam. It is just an opportunity for some free miles or travel points for spending a bit of time online filling out surveys.