But...
I had similar "who would ever use that?" thoughts about Foursquare when it launched, and had to revisit my feelings after seeing its success. It turns out that even if there's little value in the actual services provided, people really like the types of game mechanics that location-based apps make possible. This, IMO, is where GiftRocket should be focusing: they really should be pitching a game experience instead of a mere gift card.
I can easily imagine people setting up scavenger hunts, races, treasure maps, etc., if the site was set up to make that sort of thing easy and fun. You could even set up entire Amazing Race-style multi-leg races if it was done right. There are a lot of possibilities, and I could see the same sorts of people that get really into Foursquare getting really into this.
Don't get me wrong: I think this is a pivot that may need to be made, it's not where they are right now. As-is I don't see much emphasis of any game-mechanic in the marketing (and for that matter, the most likely fun applications, races and multi-leg treasure hunts, don't seem to be possible to construct), and the exclusive focus on sending people to businesses may not turn out to be the best approach unless they can start to sign on businesses to sweeten the deal (I'm sure they can line up things like 10% off if you redeem a gift card there or something like that). But even that's a bit of a shift, and it puts them more in the discount-seeking business than the gift card one.
Or I could just be wrong. This is a YC company, so they're sure as hell going to get enough eyeballs to battle-test the idea, and maybe the sheer novelty of it all will lure enough users to make this work even if they just stick with the current model.