From Concentrate Software has announced the release of Paperclip 1.0, a new application that lets you attach "Stickies"-style notes to your documents. It costs $9.95, and a demo is available for download.
Paperclip operates as a menu bar application, enabling you to attach notes to your documents the same way you might do so in real life. Those notes can contain text, images, movies and other media. The notes are document-specific, so they'll be available when you switch applications.
System requirements call for Mac OS X v0.5 or later. Paperclip is a Universal binary.