From "Collegiate Baseball":
July 2004, article entitled "Young pitchers at risk for serious injuries"
Recommendation #6:
"Pitchers should compete in baseball no more than nine months in any given year as periodation is needed to give the body time to rest and recover. For at least three months a year a pitcher should not play any baseball or softball, participate in throwing drills or participate in other stressful overhead activities (javelin throwing, football quarterback, softball, competitive swimming, etc.)."
Another interesting recommendation, # 8:
"Pitchers should be discouraged from participating in "Showcases" due to the risk of injury. The importance of "Showcases" should be de-emphasized, and at the least, pitchers should be permitted appropriate time to prepare for the display of their skills."