Orion tips his hat to bj and Dubbya...
well said!
fctoma, most of us can atest to taking a site built with tables updating it to a table-less design and watching our rankings jump. Some of that may be simple 'activity' on a site which most of the SE's like to see but when the content remains identical it just works.
All the SE's tell us that tags are important.
If you're not using <li> for your nav menus then it's not accessible to speech browsers and many mobile browsers.
Using CSS you can place your <heading> tags where you want the SE's to find them and style them how you want them to appear.
there is just way too much that you can do with CSS that you can't with tables.
With the major SE's starting to put a premium on accessibility, you have to use CSS div in your layout to take advantage of that properly.
Like bj and other's here have mentioned it's not a huge gain in
SEO right now, but in marketing and in the future it almost definitely will be.