Just thought I would point out, as I am also on a MAC...
the downloaded ZIP file for this mod once opened on a mac does NOT contain a .minecraft folder as per the instructions. There is a .classes folder, a txt file and a unix executable file only in the zip. I am sure this is probably some problem with the way Mac handles the extraction of the file, but I thought I would point this out for the mod developer and possibly someone else more advances with a mac than me to solve. Basically, if you are on a mac you will probably need to hold tight for a solution.
Hope that clears it up for other people.