This is a very helpful, well, summary of OS X's built in summarize service. It uses rules to reduce text into a shorter form, in hopes that you can skim and still get the gist. I've used this some early on and it really is helpful in some contexts.
It would be hard to rely on such automated truncation in many regards, however the idea can easily find import in some uses. Services in OS X Snow Leopard are about to be much more functional and user friendly, with customized and context-sensitive menus and contextual menus. I'm excited about this.