First of all, let me just get this out of the way, I can definitely see this kid staying at catcher, at first, I was a little bit concerned because they were numerous reports (from BA and BP mostly) saying that he looked like Travis Hafner already, that's just simply not the case, he looks very lean and athletic, I mean, I know he's only 18, but Josť Molina looks bigger back there.
Now onto the home run, what a shot, 0-2 count, facing the lefty Darensbourg, cut-fastball that was supposed to hit the inside corner sailed over the middle of the plate, Montero stayed inside with his hands and went the other way with it, it looked like a pop up right off the bat, but the RFer kept going back... and back, then the ball went over the RF fence, the wind definitely helped that ball get out of the park, but the raw power was evident. Reminded me of Tabata's HR last spring vs SEA.
Defensively, not really much to say, he wasn't really challenged back there over his 4 innings of work, one thing I noticed is that he's not very good at framing pitches, other than that he looked solid. Very strong wrists.
By the way Montero's setup/stance is very similar to Shelley Duncan's.