deadsea - 11:12 am on Jan 22, 2013 (gmt 0)
A few years ago, I took a massive site (22 million pages) through a full site redesign. We kept the urls, titles, and meta all the same. Pages kept their main content the same. The design was completely overhauled with new header, sidebars and footer. We were very concerned about any SEO problems and made sure we did a lot of QA to make sure the stuff that wasn't supposed to change, didn't change at all. In the end, we pulled the switch, made the change, and Google didn't see to notice at all. Our crawl levels stayed constant. Traffic levels didn't even flicker. This kind of change can done without having an SEO effect.