Baseball America just did a draft study on which teams have been the most successful at drafting and developing major league talent. While I think the study has its flaws (e.g. Texas would get credit for Edwin Encarnacion despite the fact that the Reds clearly developed him and Toronto ranks first overall, mostly due to players who've come up with other teams or thrived elsewhere) it does break down the number of everyday players (502 plate appearances in a season to qualify) and starting pitchers (162+ IP in a season) each organization has churned out since 1995.
More interesting, to me, is when they sliced it up along college/high school lines in taking a deeper look at the results.
Though it lacks qualitative information, college/JC players far outnumber high school players. Here's the raw numbers:
College/JC - 219
High School - 106
College/JC - 262
High School - 127
Now, there's probably a good number of high schoolers from recent drafts yet to break through. A study from 1991-2000 would probably be a more accurate slice, but I find the results stunning. While it ignores relievers, I think BA chose two excellent yardsticks. You had to do something right at some point in your life to merit being a BA or ERA qualifier. Somebody thought you were worth being one of the main contributors on your team, even if you ultimately fell flat on your face.
I never would have guessed it would be so lopsided toward the college players.