Macromedia has released an SDK that allows search engines and developers to parse SWF files and extract text and links.
The FAQ states that MM are working with a number of companies but no announcements yet.
Atomz Search and Google are two of the search engines I know that already are harvesting content from SWF files. Google so far has only extracted links from SWF files, but might be tempted to add more search capabilities to their search engine. The question is how easy it is to find and structure to the text in the SWF files.
John Dowdell has some intersting comments about SWF and search engines. Especially to those that might think that this is the solution for all their search engine problems.
Even with plain text content you just don’t dump it out there and hope it gets indexed as you wish — if you care about such things, you optimize the page to be recognized by various engines under the desired searches. With SWF you’d do the same thing with the HTML page holding the SWF.