Well, it turned out that some of them weren't necessarily scams, and there were whole forums dedicated to actually completing the offers, keeping proper documentation and claiming the prizes.
Most of the free trial offers validated your credit card for the initial free month, and then made it incredibly difficult to cancel the service. So I'd just sign up with a ShopSafe number that was valid for 1 month with a $1 limit.
Typically, instead of actually shipping you the Xbox or whatever the prize was, if you completed the offer they'd just send you a check. The year after I got out of college when I had plenty of free time, I managed to get about $1,200 thanks to those offers and ShopSafe.
It's not a feature I'd use enough to have it dictate my overall credit card choice, but I'd love it if more issuers added to their products.
