To Flash or not to Flash. If you're Madonna or Coke... someone with a big well known brand, you really don't need to worry about your rankings and therefore don't need to worry about a Flash site or splash page.
'The number one reason for getting rid of our splash page was that it turned away at least 25% of our site visitors, sometimes more. This percentage is has actually been researched and it turns out that at least 25% of site visitors will immediately leave a site as soon as they see a “loading” message for a Flash splash screen (even if there’s a “skip intro” link). Our access logs confirmed this for us and this over all the other reasons caused us to get rid of it. The opportunity to “prove our creativity” was not worth the loss of such a high percentage of visitors.'
Search engines see text, period. Having a site with no content (text) gives them nothing to index, therefore killing your chances of being found by search engines. By nature, Flash has no indexable content that the search engines can see. To tackle this problem some people create an HTML version of their site. This gives the search engines something to sink their teeth into. You might want to read the articles below if you're considering a Flash site and want to be found in the search engines.
Related Links and Resources
Facts of the week: How to get high rankings with Flash sites
Flash: 99% Bad
How to Convince a Client They Don't Need a Splash Page by SEOMoz.com
Flash and SEO by Matt Cutts
It doesn't help much to optimize your Flash site
Uproar over Anti-Flash Intro Survey Results ( 80% of Consumers Hate Flash Intros ) by MarketingSherpa