I'm pretty certain that ComingSoon.net only displays studio-released synopses of movies. If so, the comprehensive preview site (probably my favorite) has the official plot information for Watchmen. The synopsis doesn't go into too much detail, but it gives enough background to say all it needs to. For instance, it mentions that it takes place in an alternate 1985 and that the American-Soviet relationship is very tense. It also gives Rorschach by name as seemingly the protagonist of the story, while the Comedian is referred to as "one of his former colleagues" and the rest of the 'masks' are described as "a ragtag group of retired superheroes." Ragtag? Sounds like they're going to start a football league and have some sad-state actor coach them all. The last sentence of the synopsis, as could be expected, includes the following: "who is watching the watchmen?"
In a couple weeks we should (hopefully) have an official cast list to go with this official synopsis. So far, we're expecting the cast to include Patrick Wilson, Billy Crudup, Jude Law, Jackie Earle Haley, Thomas Jane and Gerard Butler (I don't believe the Kate Winslet rumor at all). With director Zack Snyder expected to appear at Comic-Con, he may give more details about the plot, too. I figure that most everything from Alan Moore and Dave Gibbon's graphic novel will end up on the screen, maybe in an abridged way, except for the stuff with the newsstand and the shipwreck comic book story that parallels the real plot. Screenwriters David Hayter and Alex Tse may also have eliminated some of the back story and/or the slow parts involving Dan/Nite Owl and Laurie/Silk Spectre. I think Jon/Doctor Manhattan will also have his costume throughout, or at least some pants. Filming on Watchmen is set to begin in a few months, and the movie will hit theaters next summer.