"How does it compare to a mouse?"
From what I experienced, it seemed to be more precise than a mouse, but it's also much faster because it requires only a much smaller movement of the hand to achieve the desired effect. You just instantly point the controller at any part of the screen and bam!, that's where you're looking.
There is no lag.
There is no error.
It took a while to get used to the idea of how little effort is required to play a game with this controller. I kept wanting to lean forward and move the controller closer to the screen, and it took some practice to just sit back and just calmly move my hand ever so slightly.
At one point, someone said, "If you were to play a game with this against someone using a mouse, they'd have no chance against you." I had to admit it was true.
I've been using a mouse and keyboard for gaming for almost as long as I've been a gamer. I've logged over 80 hours so far in Battlefield 2 and I have a level 60 World of WarCraft character. If somebody had tried to tell me before now that a better controller would come along, I would have laughed at them.
But it only took me 5 minutes with the Revolution controller to realize that I don't need to use a mouse ever again.
Let's take a first-person shooter as an example. With a flick of the wrist, you can completely change your aim point from one corner of the screen to the other. Changing your aim point that way would require you to move a mouse all the way across a gamepad and could potentially take up to several seconds of pushing on a thumbstick with a standard console game controller.
Add to that the fact that the controller can correctly interpret roll (rotation of the controller clockwise and counterclockwise) and movement toward the screen or away from it, and you start to get an idea of the universe of new gameplay possibilities that Revolution games will be able to explore.
http://www.rewozz.com/viewtopic.php?pid=115
Edge:
http://www.edge-online.co.uk/archives/2005/09/nintendo_starts.php
And this new, precise control system could well be the first time that mouse and keyboard-style precision is brought to console gaming by a native controller.