gamepro has finished the game and says there are some long ones but none of them are even close to the 90 min.
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Update: Game journalist Sid Shuman has stated that while MGS4 includes some lengthy cutscenes, none of those cinematics comes close to the 90-minute mark.
"I've completed the game twice, and am the author of the forthcoming [GamePro] review," Shuman told GamePro. "Some of the cut-scenes in the game are elaborate and occasionally lengthy. But not a one, to my recollection, even approaches 90 minutes."
http://www.shacknews.com/onearticle.x/52828