Originally Posted by Jon

Despite the fact that CSS is a recent SEO buzz word, it seems most SEO gurus tend to feel that the main SEO advantage CSS has is smaller file sizes so that search engines spider quicker, which isn't always needed and with some css implementations that isn't even the case. Search engines are concerned primarily with the keywords and content within a site, not the html code used to create it.

That said, in my opinion the biggest advantage is loading relevant content to the end user quicker. CSS is the way of the future and as CSS adopts better standards and has increased better cross-browser compatibility, it will allow much more flexibility and cleaner code, but in my opinion and experience isn't a large factor in SEO position at this time.

Here's an expert from Jill Whalens, a highly respected SEO consultant from highrankings.com