I don't own the mouse, but I saw this review on the us amazon site:
Back button advertised but not supported, November 7, 2007
By D. R. Schumacher "subsailor" (Hobbs, NM USA) - See all my reviews
I bought this mouse for two reasons...Bluetooth (thus no receiver needed) and the back button.
When I set up the mouse in Mac OS X 10.5 (which is listed as a supported OS for this mouse, right on the package), there is no option to assign the "Back" button. The "Back" button does not work.
I called Microsoft support, they researched the issue and (to their credit) called me back, and confirmed that the latest Microsoft mouse software does not support this mouse with regard to the "Back" button.
The tech supervisor even told me point blank that the mouse was released with knowledge that it did not fully work.
Other than this missing functionality (which is frankly all I wanted this model for), it works fine. However, be warned...the features and compatibility listed on the package and here on Amazon do NOT reflect the actual features and compatibility of this mouse. In my opinion, this is false advertising, thus despite it's otherwise good quality I only give it one of five stars.
I saw this mouse at best buy today, and was considering it. I am going to wait a little while longer for some other dongle-less bluetooth mice to be verified to work with leopard first before buying one.