For me, one key difference between the 15" and the 17" machines is the fact that on the 15" ones you can only have a hard drive that is 5400 rpm whereas with the 17" you can also choose a 7200 rpm. Yes, there are differences in the drive size, but to me it makes more sense to have the 100 GB 7200 rpm drive and then plug in an external drive of any size for additonal storage space than it does to go with the 5400 rpm drive, regardless of size, as chances are that you'd still need to add an external HD at some point anyway.
My 15" CD MBP, purchased in May 2006, has the 100 GB 7200 rpm drive and I am sorry to see that this option is not available to consumers preparing to buy the C2D 15" machine. If I were in the market for the C2D MBP I would be leaning heavily towards the 17" one just because there is the option of the 100 GB 7200 rpm HD with that machine.
My 15" CD MBP, purchased in May 2006, has the 100 GB 7200 rpm drive and I am sorry to see that this option is not available to consumers preparing to buy the C2D 15" machine. If I were in the market for the C2D MBP I would be leaning heavily towards the 17" one just because there is the option of the 100 GB 7200 rpm HD with that machine.