What flash will not do though, is make your site more visible to the search engines. Its a subjective judgement call at the end of the day, but its important for clients to realise that.
Flash sites can be SEO'ed (article here but Jonathan Hochman) but they will never be able sustain high rankings as all you can do is an off site campaign.
I usually advise clients against full flash sites but a little here and there doesn't hurt too much.