I have two sets of Microsoft's Bluetooth Keyboard / Mouse. I *love* the mouse. I never thought I'd use the side buttons, but now, it's second nature.
Overall, I like them, but they have their quirks:
* The Bluetooth tranceiver for the computer will not directly install on XP SP2. It was "no longer supported" or something like that. I had to buy a separate bluetooth dongle.. 50 more bucks.. It *does* work on an SP2 that was upgraded (and previously installed).
* The original Bluetooth Dongle would only work for the keyboard and mouse, no other bluetooth devices (that I could figure out, nor my friends).
* Battery Life of the mouse is about 3-4 weeks..
* Takes a few seconds on boot for the keyboard / mouse to "kick in". Doesn't happen with my Missus' Logitech keyboard / mouse.
It definately has a good feel to it, though. I wouldn't recommend buying them, but now that I have it and know how to work around the quirks, I'm staying with them for a while.