Running 2.2.0 on Touch, I just had it freeze on me.
Doing normal reading, as I have been for hours. Did a forward page tap. Page did not go forward, a word above where I tapped is dictionary underlined (no thumbs), the bottom dictionary menu is displayed (pencil, dictionary, mag glass, facebook on the left, x on the right. No tapping will unfreeze the screen.
Home button worked correctly, in that it bookmarked the page and went to the home screen. But the screen is still frozen.
Putting it into sleep mode with the power switch worked. Woke it up again using the power switch, screen still unresponsive.
Powered off using the power switch. Powered back on. Back to normal, the screen works again.