This information is in the forums, but it's rather hard to find. It really should be on the Troubleshooting page (http://arduino.cc/en/Guide/Troubleshooting
I recommend adding something like the following to the Troubleshooting page in the Drivers section of the question: 'Why can't I upload my programs to the Arduino board?'
---suggested text for Troubleshooting page---
+ On Mac OSX you can tell if the FTDI drivers are installed from the list of serial ports in the tools menu. If, when the board is connected, the list contains only the following:
then the drivers are NOT installed (these are standard Mac ports). If they drivers are installed there will also be ports with names like:
You can download the latest FTDI drivers from: http://www.ftdichip.com/Drivers/VCP.htm