Lyrad already posted a fine review of 300, but I thought I'd throw in my few cents.
I saw it the other night, and the thought that kept running through my head was that the film could have taken place entirely within the imagination of a ten year old boy. (Or your average neoconservative.) My little brother and I fought these sorts of battles countless times, wildly swinging our fence-picket swords, as well as a considerable array of other home-made melee weapons, at the oncoming horde, tumbling and rolling around our small side yard in South Nyack, fighting back wave after wave, taking arrow after arrow until we... just... couldn't... go on. (There's probably a secret rec room at AEI with foam-rubber swords and cardboard shields for just this sort of play. They call it "The Lab.")
300 is about as good an illustration of Edward Said's ideas about Orientalism as I ever expect to see on film. I should say first that I disagree with Said's overbroad characterization of Western scholarship as being in the service of empire, and think it's been amply demonstrated by Said's critics that work relating to the Orient has been rather more diverse than he gave it credit for. Then, as now, imperial governments and their intellectual servants seized upon scholarly work which served to justify their particular aims, and ignored that which didn't. (Please see: Iraq, invasion of.) As he was neither a historian nor a political scientist, but a professor of comparative literature, I find Said's work most compelling when he focused on the use of literature and art in the production of knowledge and the maintenance of Western popular assumptions about the Orient. 300 could function as Exhibit A in this regard. The Greek (rational, well-organized, frequently bathed, and white) and Persian (prone to magic, a horde, much less frequently bathed, non-white) ethnic and cultural stereotypes are so blatantly offensive that they come very near subverting themselves. There were parts of the film that really made me wonder if the filmmakers were indeed winking at the audience, such as the Spartans' "Before we sally forth in defense of reason, let's consult the Oracle!" bit, but I don't think so. Did this spoil the film for me? Not really. I mean, did you see Xerxes? That dude was huuuuuge.
Anecdotally, I find it interesting that quite a few people I've spoken to have criticized the movie's representation of the Persians in terms that that I can only describe as Saidian. That is, they recognize the role that popular culture plays in reinforcing assumptions about the Other, and the way that these assumptions service certain political ideologies. The fact that some tech dudes at a party, who had never heard of Edward Said, were casually pointing these things out to me between tequila shots can, I think, be seen as a victory for the better parts of Said's work.
Of course, the majority of people who see the film will not be not over-educated, pointy-headed liberal types who sit around increasingly-drunkenly discussing representations of the East. (That is a pleasure to be found only in select regions of this country.) I suspect more will see it in Victor Davis Hanson's terms, freedom versus tyranny, even if it is only the freedom to discard one's imperfect children and raise the rest as killing machines/sperm donors in a proto-fascist nightmare society, and will fold the film's negative portrayal of the Persians into their pre-existing anti-Iranian paranoia. The vast majority, however, will see it as simply a bloody good time at the movies, which it is, even if it didn't quite gel, in my opinion. Like a soupy merengue, though, it's still really tasty.