Indeed. I don't know about the movie as I haven't seen it but the pontoon bride over the Hellespont was pretty major for that time. Quite clever.
Greece was hardly more than a handful of city-states who had a hard time defending the country because the concept of "Greece" as a nation had not yet taken hold. Sparta sends a mere 300 troups to defend the homeland? Actually kind of pathetic.
But the facts don't make for a compelling movie and movies are a bad source of historic fact. Doesn't mean it's not entertaining and I'm looking forward to seeing it, but still it is just a freaking movie and I don't think I'm going to rely on it to support my world view.