For all users who want to downgrade to a version of minecraft lower then the current one out (i.e 1.1, 1.2.5, 1.3)
I apologize for not knowing how to downgrade on a MAC, this is for PC's.
How to find the download and downgrade on a windows computer:
1: Find a .jar client of minecraft for the version you want to downgrade to (1.1, 1.2.5 etc).
2. Click on the "start" icon on the bottom left of your screen. then type in the search box "%appdata%" then a folder should pop up that is called "Roaming" then go to the folder inside roaming that should be called ".minecraft" unless you renamed it.
last go to the folder "Bin" inside of .minecraft that will open up a folder that has some jar files and folders inside jars should be named "jinput", "lwjgl", "lwjgl_util", etc.. and "minecraft" files should be named "md5s" and "version" and 1 folder should be called "natives" Notice most of these files are not changed in the process.
3. Now take the jar file named "minecraft" and delete it. (that will be the current version you are running, I suggest copying it to your desktop before deleting it. DO NOT DELETE ANYTHING ELSE as it will mess up your Minecraft.
4. Take the new .jar version of minecraft you want to downgrade to and drag it into the bin folder where you just deleted the minecraft.jar. then restart Minecraft, on the bottom left of Minecraft it should tell you the version you just downgraded to.