[Warning, may contain spoilers!] Several hours ago, my review of Episode III was published on Novinky.cz (in Czech) and I already got feedback from three people who are angry about the supposed spoilers. Specifically, they didn't know that Obi-Wan fights with Anakin and/or that Anakin gets badly burned in the lava. I think I am not "Star Wars geek" but I presumed this is kind of stuff anyone who even considers seeing "Revenge of the Sith" automatically knows.
One of the benefits of living in former communist European country is the fact that regular moviegoers in Czech Repubic will see the movie at 8 pm local time on Wednesday, i.e. around noon U.S. time, i.e. before the U.S. premiere (if I am not mistaken).
(The image shows fans from Czech Star Wars Universe attending the premiere of Episode II.)