Loved this movie. I also thought James Franco stole the show. I almost feel like he had to have ACTUALLY been high the entire movie (either that or he's a way better actor than I thought). Danny McBride was just about as awesome. After seeing him in this and in Tropic Thunder I'm convinced he's destined to be the next big comedy movie star.
after first saying i thought it was more of a wait for video movie, i heard it was good. so i went to see it "fully prepared" and it was worth seeing. definately alot of "inside" humor (anyone who isn't a regular smoker might not really "get" it all) that was definately appreciated by the crowd i was with. bonus points for lots of quality violence that i didn't expect. this is an action movie! bake yourself like a cake and check it out. as far as the actors actually being stoned, if they really smoked that much pot that good they would have never left the couch.but kudos if they pulled it off.
Let's see: 2008 Arthur traveled back to 1992 to steal the Catalyst from 2008 Hiro. He was able to time travel because, as others have said, he had Peter's time travel ability. He didn't have to take anything (directly) from Hiro for that.