Make sure you are in your personal Library folder and not the System /Library folder.

An easy way to do this is to open a finder window, and then from the menu bar, select GO and then hold down on the OPTION key. You should see the "Library" folder appear (it's normally hidden). Select it, and your user ~/Library folder will open.

From there just look for a "Mobile Documents" folder.

Note that some of these folders will have non-obvious names. where you may see some for Keynote, Mail, Notes, Numbers, Preview, etc. Each of those apps that are Cloud aware may have a folder here. You will also find a few with random alphanumeric strings. Sometimes you can figure out the app that owns these from the names, sometimes not ;)

Thanks for your response. I had a conversation with the author in the meantime and it only works with Mountain Lion, I have Lion. I didn't realize it when I posted.

Paul