The 13" has the core duo chip said to be more energy consuming, but the 13" gets an extra hour of claimed battery life compared with the 15" and 17" models with the reputedly "more efficient" CPU chips. I wonder, has anyone tested the three sizes of Macbook pros, with the assumption that the 15" and 17" will not be called upon to switch to the Nvidia graphics? In that sort of comparison, then would the 15" and 17" beat the battery life of the 13" MBP? A test like that would suggest what would happen if the 13" got the i-core CPU-GPU package (but not the 2nd nvidia graphics chip, since the 13" cases haven't room for that). Is there something about the details a d the arithmetic of cramming a battery into the leftover space... in laptop cases all of similar inside depth... that somehow worked out a little more favourably in the 13" MBP?