How to extract icons on OSX
I downloaded great icons from http://iconaholic.com but could not convert them to PNG. The info dialog said that it was a Unix Executable. After reading multiple posts on the Web, I finally mashed them up into a viable solution. No additional software is necessary.
Select the file or the application that has the icon you need. Open the info dialog by selecting Get Info from the File menu (Cmd+I). You will see the desired icon at the top-left of the dialog. Click it and it will be outlined in blue. Now copy it (Cmd+C). Open the Preview application and choose New From Clipboard from the File menu (Cmd+N). You can navigate to the desired icon size and select Save As from the File menu (Cmd+Shift+S). Select the desired file format and save!