I finally broke down and bought an Apple Magic Mouse a couple of weeks back to replace an aging Logitech MX Revolution. I'm happy with my new input device, but I suspect it will be the last Apple mouse I ever buy. That's because I'm convinced that this is Apple's final mouse.
When I first started using it, I thought of the mouse as a hybrid device that cleverly combines old and new input ideas. After using it for a while, I've started to think about it as a transitional device. The Magic Mouse isn't about the mouse at all. It's all about the Multi-Touch surface.
My guess is that Apple will soon proclaim the mouse dead and drop it from their product line. Only the Magic Trackpad will remain for desktop computers.
Is the Magic Trackpad a superior input device? Based on my experience using the Trackpad on my Macbook Pro, I'd say it's better for most tasks but not as good for tasks that require fine control. The Multi-Touch, finger-driven interface is great, but it would be even better to have a large Trackpad that could transform into a Wacom-style pen tablet device. Perhaps a gesture could toggle modes.
Of course, even touch surfaces may someday be obviated by eye- and voice-controlled desktop computing. I can see how such future tech might work well for routine tasks, but I wager we'd still need some sort of physical input device for precision work (e.g., detailed selections, drawing). I bet that device will look a lot more like a Trackpad than a mouse. It could also look like an iPad running a Trackpad app.