The space available becomes more useful for the plethora of multi-touch gestures that Apple provides. All the obvious actions, such as pinch-to-zoom, rotation, and three-finger 'forward' and 'back' navigation are present, but Apple has also added the Magic Trackpad-specific option to have a three-finger drag move windows around. Unfortunately to enable that you have to sacrifice navigation gestures which is a poor tradeoff - we'd rather lose the four-finger Command-Tab gesture.
We're unsurprised, but nonetheless disappointed, by the Windows support offered by the Magic TrackPad, too. Obviously we're not expecting quite the level of OS integration the Magic Trackpad as with OS X, but the option to at least bind gestures to actions within Windows would be appreciated.
While the default multi-touch functionality is everything you'd expect, the real magic actually comes with third-party programs - BetterTouchTool is a prime candidate - that let you assign your own multi-touch gestures. The Magic Trackpad has no problem registering as many digits as a normal person could plausibly apply to it, so there's no reason to limit yourself.
We wouldn't go so far as to suggest that the Magic Trackpad is a completely viable replacement for a mouse, but if you use your Mac in a manner that fits with the device's limitations it's an interesting alternative. For general desktop use, such as browsing he web, accessing emails and editing pictures in iPhoto or even Aperture we found that the Magic Trackpad really did make things easier after we adjusted to the new input.
There's a much more natural correlation between the action of moving a finger across a touch-sensitive and a mouse pointer moving across a screen. And, while it's of course possible to make fine adjustments with your fingers when using a mouse, most movements are made from the shoulder and elbow which are both far less dexterous than your digits.
We'd be remiss not to qualify that advantage of the Magic Trackpad if we didn't point out that a stylus is an even more efficient tool for image editing and creation applications. Manufacturers such as Wacom have long-hence perfected such inputs, and Apple's Magic Trackpad isn't about to usurp them. But then the Magic Trackpad isn't trying to replace graphics tablets, so that's hardly a criticism.
Apple's Apple Magic Trackpad is pretty expensive for an unnecessary peripheral, but it works as advertised and can even make general desktop activity a little easier than a mouse at times. We've a long way to go yet before we'll be persuaded to part with our mice, but this is certainly an interesting step in the right direction.