Web pages that are designed with Flex Content, that is, using "a module that allows for flexible display of introductory text, title, and an image from any content item," are not spidered by Google, from reports in Google Groups.
What are the options, then, if you're a Flex content developer? Just like Flash content, it seems, you should make the same content available in standard HTML for the search engine spiders. This would also help those users visiting your site using a browser that is not Flex compliant.
Forum discussion continues at Google Groups.