How to mount Raspberry Pi SD card to OS X

gistfile1.txt

Install http://sourceforge.net/projects/osxfuse

System Preferences -> 
Security & Privacy ->
General ->
Allow apps downloaded from: Anywhere

Install http://sourceforge.net/projects/fuse-ext2

Open /System/Library/Filesystems/fuse-ext2.fs/fuse-ext2.util in your text editor.
Edit the line with 
OPTIONS="auto_xattr,defer_permissions"
to read 
OPTIONS="auto_xattr,defer_permissions,rw+".
Save the file (requires sudo).

Insert the SD card into your MacBook. 
It should automatically mount to /Volumes, typically the volume is named "Untitled".