Iran can go suck it. The Persian army consisted of largely unskilled, conscripted warriors that fought using fanaticism and strength in numbers. In that respect, the movie was quite accurate. Most Persians couldn't stand a chance against a Spartan, even two or three to one. They were badass.
To the above, yes, Sparta had very little to do with Salamis. The movie used real quotes from ancient Spartans, which I found enjoyable, but though it was exaggerated to an extent it was not "completely inaccurate".
Spartans were "boy-lovers", but Athenians moreso, as they found the young male body to be the ideal form and there were specific words for the older and younger males in these relationships. For Spartans, the genders were largely separated and husbands and wives rarely saw each other. Thus, out of practicality and to strengthen bonds in the troops, they did engage in homosexual encounters. In fact, upon having sex with their wives for the first time, it's been said that the woman had to go "doggy style", for lack of a more elegant description.
Despite the discrepencies, it still tells the story, albeit Hollywood-style. It's one of my favorite movies, I'll admit - and I saw it in Imax, the best you'll ever get.
I can't cite my facts, other than the fact that I've had two years' of classes on this, as well as research from major projects and out of interest. =)