Regardless of SEO, you should never use flash on the first page of your web site. Flash is ok for optional followup pages but the links to those pages should indicate that it contains flash.

Your first page needs to load instantly even on slow computers and slow connections. Otherwise you will lose your audience. You only have seconds to get someones interest.

The exception to the above is if you want to limit your audience to people who have unlimited bandwidth and fast connections, and you want to be sure no one else will stay on your site.

The first thing I do when I open a site and the first page contains flash (or auto start sound or video) is to close that tab and go somewhere else.