I love Flash. I love the creativity. The look, and feel of a flash enabled website. But..............and I get this question constantly (as I did about 30 minutes ago). Web Crawlers for search engines do not pick up on the Flash files. So if your interested in website traffic, try not to program in flash (or at least offer the visitor a choice between viewing your content in either HTML or Flash on your landing page). If you NEED to have Flash, then make it it a flash "light" site. Also, in general, a heavy Flash site loads slowly which may piss off or alienate a visitor who is in a rush to get information. If they click back quickly to where they came from (a web search) your web logs will probably not count that click on your sites page. If you do offer an HTML version make sure you use robots.txt file on the Flash side so your website isn't indexed twice. Its just good "best practice".
I can go on and on and on but I'm just too tired at the moment ;)