Designing a website in Flash destroys and real chance of ranking well in the search engines: period. Even if they can index the content you still are only a one page website with no html to give the search engines clues about the content and no internal hyperlinks with keyword-rich anchor text. If you want to rank well in the search engines don't even think about using flash. Otherwise kiss good rankings goodbye.
If someone is going to insist on an all Flash website then they might as well use it as they'll need all of the help they can get. Just as long as they understand that it won't help them rank in the search engines then they won't be disappointed.
I might add that if the site has already been up for a while, and you change it over to something that the spiders can get into, you might very well end up in the so called "sandbox" for up to a year, which will severly restrict the rankings of your major search terms. I suspect the reason for this is that Google will consider it a brand new site.
SDK will help, but what it does is export the contents of the swf file into html which the engines then read. Now the point is that how much content are you going to have in an swf? You might as well keep content in html and graphic flash elements as they are.