I have seen that many of you have issues finding the minecraft folder on a mac, so here it is.
First of all you will need to know what version/software you are using.
Click the apple logo (top left) -> About this mac -> More info... (it will be at the bottom).
For OSX Snow Leopard : Finder -> User -> Library -> Application Support -> Minecraft.
For OSX Lion : 1) Click anywhere on your screensaver (so the top bar says finder beside the apple)
2) Go to the top bar and click on "Go"
3) Scroll down and click on "Go to Folder..."
4) Once the text box has appeared type this in it : ~/Library/Application Support/
From there just scroll down till you find the minecraft folder.
If you can't open you minecraft.jar just rename it to minecraft.jar.zip, then double click and a normal minecraft.jar folder will appear.
If you wish to permanently Un-hide the Library, check out lttf's topic on the following link.
Hope this helps you guys out