Flash based sites almost never rank as well in search engines as traditional HTML/XHTML sites, and the reason is pretty simple, search engine bots are simple little programs and for the most part have no idea what to make of Flash based content. That may be about to change. Some enterprising lads are creating a framework to allow the extraction of content from flash based sites. Read about it here. I think I’ll wait until I see clear evidence that it works before I’d be converting sites to Flash.
Franki