The problem in Lion is that your Application Support library under your home directory is missing. Well, it’s not really missing. It’s just hidden from view.
To fix this problem, open up your Terminal (under Applications/Utilities/Terminal.app) and paste in the following statement and hit return.
defaults write com.apple.Finder AppleShowAllFiles YES
Next, you’ll need to restart your finder. I would recommend just rebooting your computer.
You should now be able to see all hidden files. Now you should be able to disable the automatic gain as instructed above. (I would recommend removing the MicVolume statement all together as it is simply not needed.)
Now when you run Skype you should have complete control of your microphone input level.