How do I keep my business idea from being stolen?

The Hipster PDA is a paper-based personal organizer popularised, if not invented, by San Francisco writer Merlin Mann. Originally a tongue-in-cheek reaction to the increasing expense and complexity of personal digital assistants, the Hipster PDA (said to stand for 'Parietal Disgorgement Aid') simply comprises a sheaf of index cards held together with a binder clip. Following widespread coverage in the media and blogs, the Hipster PDA (abbreviated 'hPDA') has become a popular personal management tool particularly with geeks and followers of David Allen's Getting Things Done methodology and users of the Fisher Space Pen.