is a difficult thing to do... and it can't be done with 100% accuracy.

But if you bury your head in the sand and don't even try to project 3-5 years down the road then its hard to put together a consistently good team.

If you look at Jeff Kent and Jose Vidro its pretty clear that they are both useful for 2003. But if you would choose to ignore Kent's age and say that Kent and Vidro are interchangeable parts then you would be dissapointed about 3 years from now when Kent retires and Vidro is going strong.