The first twenty minutes of the Watchmen movie was shown at the beginning of the Watchmen panel at WonderCon 2009. As you might expect, the reaction was EXTREMELY positive. One item of note from the panel: the full version of the movie, which will be over three hours long, will be released in July.

Sci Fi Wire gives more details:

The deleted shots from the title sequence include one of Edward Blake/the Comedian raising the flag on Iwo Jima in World War II and a shot of the inauguration of Richard Nixon. "They'll be somewhere," Snyder said, referring to future iterations of the movie that may appear on home video.

The opening title sequence is a montage of scenes that establish the 1985 alternate universe New York of Watchmen, based in part on iconic images from art and popular culture, including a Last Supper-style retirement party for Sally Jupiter (Carla Gugino) and the assassination of John F. Kennedy by Edward Blake/the Comedian (Jeffrey Dean Morgan).

As for the three-hour 10-minute director's cut, Snyder said that it would restore a sequence of Hollis Mason's death as well as "other bits and bobs ... a whole lot more naked blueness in it, too." Snyder got notes from Warner Brothers to cut some of the shots of Dr. Manhattan's blue, uh, manhood, as well as trim some of the film's graphic violence for the two-hour 37-minute theatrical release, which he agreed to "to be fair," he said.

From Twitter:

• cplbasilisk: Opening sequences and scenes shown at the watchmen panel are incredible! Openning credits are tear jerking. Soo good!
• EdwinFabian: just saw the first 20 minutes of watchmen (give or take) it's nuts! very true to the comic so far.
• jiGGafellz: If the opening sequence of Watchmen is indicitive of anything, then it's gonna be phenomenal.
• MeanOldPig: The Watchmen opening credits are really good.
• buymagicfish: Just watched first part of watchmen w/ @kimevey n @briankameoka stamped approved
• briankameoka: #wondercon saw opening and a bunch of #watchmen. Gonna be so awesome
• jayzombie: I am in the same room with the ENTIRE cast of Watchmen. Can't. Breath. So. Excited!
• plasm0: I'm still not exactly sure why #Watchmen was considered "unfilmable" and impossible to make? Can someone explain?
• nerdcoregirl: Just watched the first 15 minutes of Watchmen at #Wondercon09. I'm actually getting excited about it now!
• nchan: Wow they just showed 30min of the watchmen at the wondercon panel. That opening credits sequence is SO awesome.
• gizmogladstone: jjust saw 30 minutes of watchmen. awesome stuff right there. next week, i am THERE
• zepoldesign: Just saw the first 15 mins of Watchmen. Amazing!!!
• geeksugar: Just saw the first 30 minutes of Watchmen. Zack Snyder is the cutest director ever!
• L0u13: Gug first 20min of watchmen awesome.