I still think the price of electricity is pretty much the only thing that will determine the price of this coin for now. This is because you can make more coins for that cost in the near future.
As there is huge variation on the price of electricity, even 1c difference in kWh will make a 5-15% difference in the purchase price of the graphics card.

Still, there is one even bigger issue we haven't seen much talk about. It's the fact that anyone could start selling whatever hardware or goods for GPUCoin right now!
And in a sense it already happens. Just check out how many GPUCoins you need to convert to BTC to buy a 400usd graphics card at TigerDirect: 400usd = 0.63BTC = 2.1m at 30 sat.

So buy up all the GPUCoins and then you can control the price. At the current price 13 billion coins will set you back 6200 graphics cards, 2.5M usd or the sole use of a large nuclear power plant output for an hour ;-)