Robert_Charlton - 7:18 am on Jan 23, 2008 (gmt 0)

I have done a before-and-after comparison on a site that was semantically structured and naturally ordered, but set up in tables with some nav links up at the top. We went to CSS positioning and moved the nav links down to the bottom. I noticed no change in rankings, but I'm not willing to generalize from this and say that CSS positioning doesn't make any difference. This was just about a year ago.

Some years back, on the other hand, prior to CSS positioning, when I had to use the "table trick" to get the left nav out of the way, I would often observe a one or two-place move up in rankings after the table trick got the nav text out of the way (and put our H1 up right after the body tag).

One experiment that would be interesting, but more than I'd want to subject a client's site to, would be to change positioning of page template elements on some pages, but not on others, and see how Google reacts.