Currently the only things differentiating between the stock Macbook and the 13" MBP is build quality (unibody polycarbonate vs unibody aluminum), Memory Cap (4gb max vs 8gb max), default HDD size (the MBP is actually smaller), and the Pro has Firewire and a SD slot.
Granted the price difference between the MB and the 13" MBP is only $200, but I think the perfect way to distinguish between the two is IPS. Seeing this manifest itself in the iMacs is really unexpected to me given the industry trend as a whole to keep displays as cheap as possible (I was previously just hoping for a simple bump to 1680x1050 on the 15" MBP, which is what I own and will likely buy again in the future), but this gives me hope that better panel technology in the laptops is actually a potential option.