If you have a well established and known-all-over-the-world website like YouTube (which Google owns anyway) or BMW you don't really have to worry about decreasing your SEO efforts with flash. Those sites already have tons of backlinks, site authority, traffic and PR. But for most of us who are still trying hard to get ranked in the search engines, every little bit helps. And for now, flash is not good for SEO. It may not always be bad, but it definitely doesn't help.