I'd try to play it like stored value.. you don't pay tax on gift cards right?
I don't think gift card can loses or gains value if you let them sit. I'm pretty sure a 100$ gift card will always be worth 100$ no more no less. We can't say that about Bitcoin.
How does work Facebook credit and SecondLife Linden (they have a exchange - LindeX) ? Isn't Bitcoin kinda like those virtual currency?