Decent but not hardly known as you stated before.
If you mean by developing=buying and nurturing, we've done it with countless of players. You can put Cech, Robben, Drogba, Duff, Joe Cole, Gallas in to that category as well. Unless you discount those who reached a certain age. The players I mentioned above were able to realize their potential and reach their peak when playing for Chelsea(except Robben who's still doing well with Bayern), yes most of them were sold which I did disagreed with, but they were the ones who wanted to leave ala C.Ronaldo.
And about the players I listed, I thought you were talking about our youth development, which to me is still promising.
So you're making a point about the current state of our teams then? We've only paid for one world class player in three years. And that's Torres. David Luiz/Ramires are hardly world stars currently but they cost us because we didn't want City to hijack our bids at the last moment, e.g - Robinho.
With Ramires and Luiz playing with us, who are competing for everything each year, with a world class training facility in Cobham and a respected coach like Carlo(who's done his mojo on Kaka, Sheva before), I can honestly see them developing into world class players like Nani, Vidic, etc.
When Jose was here I thought he did a great job in transforming a group of potentials into winners. I'm sure that can be considered developing as well, as you claim with the likes of Evra, Vidic, etc.
But we had to deal with his going, and with Fergie still around we won't know whether Utd will face the same freefall we did when Fergie decides to call it quits. Barca had always put their philosophy first over success, which doesn't guarantee a continuous level of success, but they've been patient and its paying off. Madrid is the exact opposite.
Utd has always been successful under Fergie in recent times. The only thing with Utd as a club, as I mentioned above, that they haven't been tested with a new management that will be inevitable in the future.