This is the most organized, user friendly coupon/deal website I ever visited and participated in.
Users contribute coupons they see through newsletters, other coupon websites, etc. The result is a nice collection of discounts available for the public to enjoy.
You do not have to register to submit or use coupons, but if you do join, some "extra features" are available.
Some stores blocks user submission of coupons, and RetailMeNot respects that, therefore, you cannot submit coupons or find coupons for every website online, but it also shows that RetailMeNot is more legitimate than some other coupon sites out there.