There's no doubt that duplicate content is a problem for search engines. If a searcher is looking for a particular type of product or service and is presented with pages and pages of results that provide the same basic information, then the engine has failed to do its job properly. In order to supply its users with a variety of information on their search query, search engines have created duplicate content "filters" (not penalties) that attempt to weed out the information they already know about. Certainly, if your page is one of those that is filtered, it may very well feel like a penalty to you, but it's not -- it's a filter.

Search engine penalties are reserved for pages and sites that are purposely attempting to trick the search engines in one form or another. Penalties can be meted out algorithmically when obvious deceptions exist on a page, or they can be personally handed out by a search engineer who discovers an infraction through spam reports and other means. To many people's surprise, penalties rarely happen to the average website. Most that receive a penalty know exactly what they did to deserve it.