I’ve tried for years to explain to clients why a Flash splash page is a bad idea. But SEOMOZ has the best comparison I’ve ever heard:
When we have clients who are thinking about Flash splash pages, we tell them to go to their local supermarket and bring a mime with them. Have the mime stand in front of the supermarket, and, as each customer tries to enter, do a little show that lasts two minutes, welcoming them to the supermarket and trying to explain the bread is on aisle six and milk is on sale today.
Don’t mess around. Just send people straight to the stuff they want. It’ll help in the search engines, too.
I don’t have to say anything else, really.