I was expecting a minimum of a 30% performance advantage against the HD 5870, that would have been sufficient to justify the heat, power, and cost negatives. 15% in my opinion doesn't justify squat. Take a game that runs 100FPS on a 5870... is it worth it to buy a GTX 480 just to run 115FPS? I think not. No game I know of requires a GTX 480 to achieve playable framerates.
It certainly does matter, I chose to not buy one after waiting eagerly for this card. I'm an avid gamer and I do plenty of Folding@home crunching on the GPU, in addition to whatever else will run on it that is neat to play with. Which means NVIDIA appeals to me for two different markets, meaning I have above-average interest in their products. But I'm not going to pay $100 more for a GPU that is only 15% faster in games, uses MORE power than a 5970 (!), and runs so incredibly hot that I would worry about running it in 24/7 loads for Folding@home (or any other super-computing applications that you mention) for extended periods.
They lost my business with this one, that's just fact.If ATI cards weren't worthless at folding (for the time being, this will change soon), I would already own a 5870 instead. Once Stanford shifts away from CUDA, it will be anyone's game as to who gets my business again.