As has been mentioned, he's quite a young player for one that is well accomplished.
Giving up a draft pick is tough, but you know that this is someone who can contribute right away as he knows the pro game, routes, defenses etc.
Picking Dez Bryant at no12 does not guarantee us a instant, top, contributor. Look at Pat Turner, whom we spent a 3rd on and he had zero catches.
Nothing is guaranteed, but the percentage chance of Marshall performing from day one is way higher than it would be for Bryant and any other WR for that matter.
It was mentioned in another thread that ESPN insider was talking about Miami giving up a 2nd and Ted Ginn. I believe this is good value, very good value. What would make it incredibly good value was if this 2nd round pick was from the 2011 draft. Maybe throw in a 6th this year as a little extra sweetner. If Ginn stays around it will be as a limited role player.
In terms of his ego.. I think there's more of a control mechanism (especially if J-Peezy-Weezy buggers off) around this team and in particular within the WR corp.
Ultimately he has been throwing his toys out of his pram because he wants paid... well... I believe he deserves to be paid. Certainly one of the top 5, possibly 3 WR's in the league. Pay him, throw the ball to him as you would want to with a talent like this anyway.. and he'll be happy. Big strong armed Henne should be an attraction and you know what, his ego/confidence could be a good thing to rub off on this offense.