Obviously from the posts here; this has had some negative effect on some, but no effect on some others. There could be a wide variety of factors why. Personally, I wouldn't risk it and is why I haven't made any site-wide changes to CSS. I've heard many state that changing their site over to CSS caused them to be deleted or at least harmed in (no surprise), google, and I cannot risk that.

If you absolutely have to make the changes, then I would only do it to a few minor pages at once, pages that are indexed in all SE's with stability. Then submit the URL's to the SE's and keep watching for the cached version of the pages to change to the new layout. Then once they do, watch their SERP's for a few weeks. If there's no change, then do the rest of the pages. If there's a negative change, then don't do it, or do it and then you'll knew to expect something bad.

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Happy Thanksgiving to all & God Bless,
-Clint
(Join Date: 2003)