Whilst following the instructions available at enlinux I had repeated errors whilst attempting to move my OS image to the SD card for the Pi to use. Specifically this line:
sudo dd bs=1m if=~/Downloads/2012-10-28-wheezy-raspbian/2012-10-28-wheezy-raspbian.img of=/dev/rdisk3
What ended up solving the problem for me (after much hair pulling) was to not use the built in SD card reader of my MacBook Pro, and to use a cheap external USB dongle. Sometimes it is the most simple thing.