Personally I feel that the duplicate content issue is a bit overhyped and that it won’t have much impact on any site that produces its own content. Google’s penalties for duplicate content are aimed primarily at scrapers and aggregators that feed off of other sites’ content.

I don’t think it’ll be an issue to have new pages with identical content as old pages on your site before the old pages are removed from the Google index. As long as you 301-redirect everything and have updated your sitemap.xml file, the search engines tend to catch on quickly and you should be fine.

Cheers,
Barry

Are there any concerns that you would have with a large site, 301 redirecting and duplicate content.

For instance if you changed the URL structure, and put up new pages with the same content and these pages got indexed they would then have the same content as the old established pages. Would this cause any duplicate content issues while the old established pages waited to be crawled and the 301 picked up.

Cheers,
Michael.