I've always been keen to bring in young somkin' guns and giving them loads of space in the first team with tomorrow in mind. And from what I've seen most debates regarding the development have mainly been discussions on weather you should keep your players or send them on loans for the soul purpose of getting minutes played... However, according to what I've observed though out the 40 or so seasons I've played through on FM11, playing well is even more vital than playing a lot... For example I've brought on Luc Castaignos on various saves and noticed something most people oversee as far as I understand. To gain maximum development he of course plays in the first team and doing well. However, if he isn't doing well his attributes will drop regardless of how many minutes he gets. So here's the trick, if you make him 'available for reserves' he'll actually develop faster on the bench in the first team rather than on the field! His far from the only example... But this raises the question on whether I'm doing something strange or if you guys are seeing the same thing?
I agree with bringing them into the first team early, their development rapidly increases. I'll often sell a key player who is first choice in his position so I can get a promising youngster into the first team and give him a chance to reach his full potential even if the youngster is 1 or 2 seasons development behind the key player. The main benefit comes after a few years when the young player has exceeded the ability of the former key player. This tactic works really well if your a smaller team moving up the leagues.
Also a youngster will often play better than his current ability if there is a great deal of potential left in him.