Yeah there are limited applications of GPU assistance for photoshop and other 2D editing apps, but really they are still very early, and very limited. Not everyone will benefit greatly from GPGPU acceleration even when it finally does come.
And it's not just CUDA based either
While there is GPGPU assistance planned for the future of photoshop, IMO, don't worry about it, get a small mid-range DX10 card from either IHV and by the time it arrives, even they will give you a little boost.
But the big focus for this stuff will be extremely large images and video. video editing is where I would start planning ahead since it's already being implemented whereas Photoshop is still a 'future direction of our app project'.
I would say without GPGPU get the cheapest 10bit supporting passively cooled card you can, with GPGPU in mind I'd say get the cheapest GF8400 / HD2400 you can that's passivley cooled.
And if you're super over-analyzing the purchae, and looking way ahead, then consider that the colour support may change in the next generation in order to support some aspects of HDMI 1.3 'Deep Colour' as mentioned in early releases. However for most people, even if they add it, they'll never notice it or the lack of it.