SEO is something that is directly derived from a well formed web, before any extra touches are added. The lines seem to blur between optimizing for the search engines, and marketing to the search engines. The optimizing part is straight forward if one uses well formed markup and keyword/key phrase rich titles and content. In fact, if you code for Accessibility, you are already coding for SEO.

Regardless whether Google of the others can see inside SWF, other user agents may not be able to. We need to code the site to provide alternate content for non-plug-in users. This will make your web even more visible to spiders.

For flash, as in any other plug-in, size and organization are major determining factors in how well indexed your web becomes. We all know that new webs are picked up very quickly. The content is what will push the site up in the results and make the site visible. But like mtheory intimates, the search engines, and the web in general, are just one small part of any well planned marketing campaign.

As has been pointed out in 'other threads' the social networks are powerful tools for marketing your web, your idea, or your product, but what the prospect sees and experiences when they reach your site is going to be the closer. Optimize with this in mind.