I always wondered this myself. Does it really make a difference though? I'm new to brewing an my understanding is that the Yeast is going to multiply anyway, so can you really put to much yeast in batch? Not trying to steal your thread just the same basic question.
For a nice explanation of overpitching yeast, download The Brewing Network's Brew Strong episode about reusing yeast. They explain a lot about pitching rates and the dangers of overpitching.