Not sure if people are still having problems. I contacted SixAxis and they emailed the following instructions. I haven't tested it out yet as I found a PC from a friend to use.
Just in case, and for future reference, here are the instructions for OSX:
1. Download libusb.pkg.tar.gz from http://www.ellert.se/twain-sane/
, unzip, run and install.
2. Download sixpair for OS X here -http://www.dancingpixelstudios.com/sixaxiscontroller/sixpair.
3. Open Terminal, navigate to the folder your file is in (i.e. if the file downloaded into your Downloads folder, you should just have to type "cd Downloads" to get there) and type 'chmod 755 sixpair'.
4. Plug your PS3 controller into your Mac via the USB cable.
5. In Terminal again, type './sixpair 1A:2B:3C:4D:5E:6F' where "1A:2B:3C:4D:5E:6F" is the "Local Bluetooth Address" that the Sixaxis controller app gives you.
6. Unplug the PS3 controller, start the Sixaxis controller app, and then press the home button on your PS3 controller.
Hope this helps someone out....