I saw "300" just few days ago and as a Greek allow me to say few things
1. It is not the first time, and I suppose it is not the last, that Hollywood makes its own "version" of history and mythology. I am glad that, at least this one, it had no "happy end" as usual, against the known facts.
2. There are plus and minus in the film accuracy. For example, there was no pro Persian conspiracy and traitors for gold inside the city. Spartan culture had no value for gold, even their coins were very heavy iron ones.
3. There are a lot of mistakes on battle. Spartans superiority was not the kung fu style of the movie, but the strong chain of heavy armored warriors (phalanx), unusual or unknown at the time, were one covers with his shield the next in the chain. This tactic with "othismos" (push against the enemy) could break big armies of lone wolfs. This tactic was used and developed further later by Alexander and Romans.
4. Of course they were not naked on battle, but... Generally in Greek armies they were some naked soldiers named "psili" or "gymnites" (same root with word Gymnasium, were athletes were naked).
5. Spartans were naked only before the battle, to wash themselves and fix their hair. They wanted to fight in a celebration
6. Spartan women, against the belief, were possibly the most free women of the era. They had their own property, they had speech on public matters and they had a lot of sports, like javelin and wrestling. If they had too, they could fight in battles and actually they had win, without their men, Pyros, the mighty king of Epirus, who came to conquer Sparta a time where men where in other war!
7. The phrase "Then we shall fight in the shade" is not Hollywood script. It is supposed said by Diinekis as Herodotus wrote.
Etc. etc. We were not there, the history was written by Greeks (but not all of them loved Spartans) etc etc
The real thing is that this battle, and few more after that, gave to this world something important: The chance to Athenians to build their culture (theatre, drama, history etc) and
Democracy so, at least, we have a name for our modern political systems
I have a sympathy for Persians, who also gave too much to the world, but I dont personally like pyramid style empires. And of course Xerxes (the great) was not this kind of freak that the movie shows.
more about the battle in
http://en.wikipedia.org/wiki/Battle_of_Thermopylae