I'm with Goksly I think on this point, technology won't outpace the uses we have for it, I don't think we'll ever find ourselves with GPU power to spare for very long, games will always make use of what hardware offers. Graphical improvements seem to follow a rule of deminishing returns, take HDR for example, its nice but not spectacular (I find it kind of annoying some of the time), yet the amount of GPU power it takes is significant, and as we see more complex rendering techniques come into play I assume this will only put more and more demand on GPUs. Oblivion is a good example of how a current game can make even an SLI/Crossfire setup of two top of the range cards have to work hard.
Complicated physics engines are also going to add to GPU load, with more items populating in game worlds, there's more to be rendered. Running physics on your primary GPU will not only steal GPU time, it'll also increase the work needed to be done by the GPU.
Thats not to say physics on GPU isn't interesting, I think its real benefit is when you can have a decent GFX card handling its normal duties and a second, passively cooled card for physics duty. While a GPU based solution may not be as powerful as a PPU, it has the definate benefit of being cheap, readily available and supported by a world class manufacturer.
