I have used iPod touch quite frequently (I don't own one, this one is used by my friend) and have been using Windows 7 on my T91MT for a few days now.
After using both these interface for "reasonable" amount of time, I do really feel that Windows 7 UI is not exactly optimized for touch screens; at least if they are the size of T91MT (8.9" screen). On a larger screen (like the all-in-ones), the story might be different.
What is good?
#1 What ever the MS marketing has advertised ;-)
#2 The super bar, the desktop and explorer arrangements are well done
#3 IE8 is quite well touch friendly
#4 The handwriting recognition and the math input panel are simply fantastic and work very well
And whats not so good?
#1: In the tablet mode on T91MT, there is no replacement for Alt-Tab or Win-Tab. I think this is a way big omission. Given a multitasking OS, I did expect to flick through open applications (only the super bar, and the live preview is *not* the solution, there ought to be something better).
#2: Any dialog with options in it to select, is simply not usable by finger, you end up using the stylus to operate it.
#3: Third party applications are not touch optimized. To me, most notably, Google Chrome.
#4: Interface elements need to scale appropriately for smaller screens with finger touch enabled.