Popular discussion in the circle of webmasters and marketers is the duplicate content penalty from Google. It all started when SEOs wanted to fool google with repetitive, keyword rich content to rank higher on the Google search engine.

Whether duplicate content penalty exists or not there are a few things to consider.

1. Google does not want to penalize a site for things that could be done by it’s competitors. (Many people think that if other sites place the same copy as the one you have, they might cause your site to be banned. This is untrue)
2. If Google sees duplicate pages on your URL (yoursite.com/page1, yoursite.com/page2 etc) most likely it will pick only one version of the page and rank only that page.
3. On the other hand if you have 300 pages with the same content, Google can easily put a red flag on your site.

So what can you do to avoid duplicate content penalties whether they are true or a myth?

1. Do not show google multiple pages with the exactly same content. I know few websites that need to have same content on multiple pages. Do avoid any misunderstandings with Google, simply ask your webmaster to place a little code for spiders to avoid that page.
2. Don’t worry about other sites using same content you have … unless there are other reasons you wouldn’t want that to happen.
3. If you must have a landing page for each U.S. state (for your PPC campaign), I’d suggest using variables to deliver different content. Ex: yoursite.com/?variable-landing-page

There is a good discussion going on about duplicate content issue on one of the SEO forums. You can read it here http://www.webproworld.com/viewtopic.php?t=64710