The BBC ran a small report on Slate PC's the other day, showing MS boss Steve Balmer showing off models from HP (ugh) and other hardware companies.
PC's in contrast can be 100% free to develop for. How MS's "Touch screen experience" will differ from Apple's touch screen "pinching" for zooming I don't think there's been any news on it. This may be the major challenge for developers to start with as obviously there's just one mouse pointer right now!
I also worry that it's an uncontrolled environment, unlike the iTunes store and not having a keyboard causes problems if trying to resolve any issues that require a lot of cmd window typing. I wonder if retro games will work, or text adventure games!
So this is hardly new in terms of technology but it is a first for PC users. I don't think it's an iPhone killer (nothing else has been so far!) But it's certainly tempting to get one when they're released...