I mention the article because people sometimes bring up the "Gillette Defense" when talking about how to fight "software" patents. The post provides a very clear explanation:
The Gillette Defence is an extension of showing the patent you allegedly infringe is invalid. If you can show that your product or process is wholly covered by a piece of prior art then it cannot infringe the patent for the new invention. The reasoning here is that you are basically using a product or process that was known at the time of the patent (i.e. you are recreating prior art) and if your product or process is covered by the patent then the patent is invalid on the grounds of novelty.