Isn't the bitinstant thing going to actually be a net neutral at best? As far as I can see it's just going to create more demand for BTC holders to use them, which means it will actually increase the sell-side of the equation as BTC are converted back to national currencies.
I think their reasoning of saying it could be huge is it can be used similar to western union for less fee, so it would increase demand for BTC from people who would never otherwise care about it.