The Touch HD has 230,000 more pixels than the iPhone, so it will be just as sharp/sharper
And this added resolution will definitely be welcome for things like web browsing. You can tilt it can get 800 pixels across - a dimension web designers were designing for just a couple years ago.
I seriously doubt that the additional resolution will be that noticeable on that size of a screen. Even 1080p vs. 1080i doesn't really start showing up until you have more than a 60" screen. Add that negligible benefit (plus the power consumption to deliver it) coupled with the ridiculously lame Windows Mobile operating system and you've got a very expensive, clunky brick, IMHO...