On this site, we do not deploy much CSS positioning. On others we try to make sure the content is at the tippy top of the source code. Why make the spider suffer, making them dig deep inside the source to find the content that the web users see anyway? We have deployed many uses of CSS on this site. The H1 tags are reformatted to match the site's color scheme, the links of course are reformatted to match.
But a cool thing we did with CSS can be found on the homepage. You see the pictures side by side, you can mouse over them and the description of the product is displayed in the box on the right of the images. You can also use the arrows on the left and right of the row of images to scroll through some more products. We did this because our client wanted some sort of flash scrolling featured product viewer on the homepage. Instead of flash, we used CSS. Take a look at the code of the page. We dynamically pull "featured products" in the database into the scrolling product viewer and use CSS to make it work. The code is clean and fairly search engine friendly. So now we get the best of both worlds, a cool and fun product scrolling viewer AND the search engines can *see* it as well.