I started using Swagbucks just within the last year. So far, I have earned over $70 in gift cards for Earth Mama, Angel Baby and Amazon.com. Realistically you can get at least one or two five dollar gift cards a month if you use the search engine daily. By daily, I mean as you normally would not searching just to get Swagbucks. I know that some people who search to earn bucks get tons of gift cards but I don't have the patience or inclination to repeatedly search and I don't search for things if I know where they are.
So, the bottom line is YES! Swagbucks gift cards can be stacked on Amazon.com so if you have three five dollar gift cards you really have $15 off whatever you are buying.