I liked my Mighty Mouse a lot (but it's not mighty anymore due to some copyright issues with the name: just the Apple Mouse now). I don't think it was my first wireless mouse (I don't remember well, but I think I had a standard wireless mouse that I gave to my sister later), but it was the first one with a trackball. I bought it not long after it was released, along with the short Apple aluminum wireless keyboard (I ordered them a little after I got my 20-inch 2.4GHz Intel Core 2 Duo iMac -- the Mid 2007 model). The freedom of having a wireless mouse is difficult to express, but adding a trackball to it was really making it easier to move on the screen. Particularly when doing a lot of internet browsing or even graphic layouts like I do. After a couple of weeks of using it, I was easily getting annoyed whenever I had to use a trackball-less mouse at work. And its round, oval shape was quite confortable to work with, even for long hours.
Unfortunately, the Mighty Mouse had two major drawbacks: poor battery life and the trackball mecanism getting dirty and difficult to clean up. Holding the mouse upside down and rolling the ball on a clean sheet of paper was the best trick I had found to clean the mecanism, but after a while it simply stopped working properly and it was getting difficult to move through the screen even for simple task. I didn't want to spend money on another Might Mouse, so I was quite happy to learn that Apple had come out with the most clever solution to solve the trackball problem for its newest wireless mouse, known as the Magic Mouse.
Unsurprisingly, Apple succeeded to build a better mouse. They gave it a new sleek design, a more sensitive laser tracking, an improved battery life and (that's where their genius came to work) they replaced the trackball with a Multi-touch surface similar to what we find on their MacBook Pro. They created the first multi-touch mouse! Not only you can move the cursor on the screen by moving the mouse (on any surface, no need of a mousepad anymore) and click or double-click like any mouse, but you can also control the screen using gesture on the multi-touch surface. There are no buttons as the mouse itself functions as a left and right two-button mouse. By brushing your finger on the seamless multi-touch surface you can scroll in any direction (up and down, left and right, and even pan a full 360 degrees). Scrolling with one finger while holding down the keyboard's control key will perform screen zoom. With a two-finger swipe you can also advance through pages in Safari or browse photos in iPhoto. It's really amazing.
I was afraid that it would take me some time to get used to its “sleek and dramatically different low-profile design” or to using the multi-touch surface instead of a trackball, but, in the contrary, it was quite easy. It's very confortable to use and I got the hang of the touch thing within minutes. It was a well spent $70. I heartily recommend it. It's simply... magic!
Unfortunately, the widget Mighty Monitor (to check the battery level of the Mighty Mouse and Wireless keyboard) doesn't work for the Magic Mouse. I hope that the widget will be updated or someone will create a similar one for the Magic Mouse. Although we can always check battery levels through the bluetooth icon in the menubar... but it's not as cool as the widget.
Update (2009-11-08): Apparently some people are experiencing problems with their Magic Mouse... No problems so far for me.
Update (2009-11-11): Still no “real” problem with my Magic Mouse but the more I use it the more I see its limitation. No complain with the laser tracking, but the scrolling with the multi-touch surface can often be difficult to control precisely. Sometime when I moved the mouse just by holding it on its sides it induce involuntary scrolling. Sometimes it scrolls too fast. It is particularly annoying when you are doing precise tasks like layout. I guess nothing is perfect. However, I still like the Magic Mouse.
Update (2009-12-08): Apparently the Magic Mouse is causing keyboard battery drain... I've been plagued by this problem since I've installed the Magic Mouse and was wondering what was happening. Hopefully Apple will acknowledge the problem soon and quickly provide a fix. Also an anonymous tipster told me that the Mighty Monitor has been updated to support the Magic Mouse. I've downloaded the update and it works great.
Update (2010-01-26): An Aluminum Wireless Keyboard Firmware Update is supposed to solve the battery drain problem...
Update (2010-06-03): Yup, I haven't had any problem since...