Here is an excerpt from Liz’s synopsis:
“If you’re planning to use AJAX on your site, or if your web site already contains AJAX, you’ll need to take some extra steps to protect your natural rankings in major search engines. As long as you follow a few guidelines, you can make AJAX work without any impact on your SEO. But if you don’t follow these guidelines, your search rank can suffer.”
I highly doubt FLASH and AJAX will always pose such a barrier to search engines but for now and the near future you will need to utilize this technology carefully to allow search engines to access content on your site.