The CNN stock quote example isn't the best example because the stock quotes have no relevance to SEO for that page, so by all means use AJAX. The trouble comes when developers place ALL the meaty content in AJAX so that if you have JavaScript turned off, there is no content. They should uses a server-side script to dynamically generate the initial content, and then use AJAX to manipulate it from there. Keep in mind it is important to us unique URL's as well. That can be a challenge as it's tempting to just have all the content on one page. This is similar to SEO challenges faced by Flash designers.