Is a sale page duplicate content?

Matt's answer:
Linda in Lakewood, NJ asks: “Should a ‘Sale Page’ be in a robots.txt file, to avoid duplicate content? These paid products are also on the site separately.” Well, if it’s just a single page, I probably wouldn’t worry about it. Because if you have all your content, and all your catalogs. And then you have one page that talks about sale items, that’s useful for users. Users like to find out about sale items. So I wouldn’t be so worried about potential duplicate content that I blocked out a single page that has the stuff that’s on sale. Now if you have 500 pages of products, and then 500 pages of sale products which are the exact same product except 2% off or something like that, then you might wanna block it. But if it’s just a single page, I wouldn’t block it. Usually Google can do a very good job of telling: OK, here’s a little bit of duplicate content, but, the page in general has a different purpose. Overall the page is different. So I wouldn’t worry about it at that level of detail. Assuming from the question that it’s really just a single page or two of sale content.
by Matt Cutts - Google's Head of Search Quality Team