You need to pop-up the operating system choices to see the OS X version. The final choice is "OS X 10.1.2". I'd call this a very quiet release, at least so far (there's no information on Mactopia about it).
The mouse program installs into /Applications, with no way to specify a directory that I saw. It is, however, just a program, so it should work fine if moved. Note that a restart is required after installing the driver.
When you launch the mouse program, you can select tabs to control the mouse pointer speed (max setting is pretty quick, but not as fast as you can get with the Turbo Mouse preferences panel), buttons (all programmable), and wheel (how many lines to scroll). With the drivers installed, my side and wheel buttons are now once again usable in OS X! It's so nice going "forward" and "back" using the two side buttons again.
I've only had it running for about 45 minutes now, but I haven't noticed any problems as of yet. Running top in the terminal shows a "Microsoft Mouse Helper" background app, but it was taking 0.0% of the CPU the whole time I watched (even while actively using the mouse).
As a side benefit, the MS driver has fixed a longstanding OS X issue for me. Previously, if I switched my mouse and keyboard over to my other machine, when I returned to the Mac the mouse would be very slow, and I'd have to manually reset the speed in the preference panel. Now, the speed setting is retained when I return to the Mac.
So if you have a Microsoft Mouse, head on over to the download site to grab the new drivers. The Macworld forum post also implied that the keyboard driver would be released next month.

