Hopefully by the time Light Peak/Thunderbolt makes it to the MacBook Air (I'm guessing this summer or early fall) there will be peripherals, such as external hard drive enclosures) that can take advantage of it. It's about the only thing that can make me upgrade to the Rev E model, particularly if the Rev E sticks with a Sandy Bridge-only solution.
Assuming the 13" Pro gets a 2.3GHz Core i5 with integrated graphics and Light Peak, I'm guessing the 13" Air will get a Core i3, which is a nice, but not overly compelling upgrade from the Core 2 Duo/NVIDIA 320m combo. Light Peak would make external hard drives as fast as internal ones, though, so it would address the Air's relative lack of storage.
Assuming the 13" Pro gets a 2.3GHz Core i5 with integrated graphics and Light Peak, I'm guessing the 13" Air will get a Core i3, which is a nice, but not overly compelling upgrade from the Core 2 Duo/NVIDIA 320m combo. Light Peak would make external hard drives as fast as internal ones, though, so it would address the Air's relative lack of storage.