Out of curiosity, how often do you swap out batteries? This came up at lunch today, and pretty much everyone at the table realized they have no real use for replaceable batteries, except for when they wear out. I had 2 for my PowerBook G4 later in it's life, and only swapped them once for more runtime.

My thought is that the companies that make the external battery packs are going to see a rise in business now, for the relatively small number of people who do need extra power on the go. The advantage these have is that they can be used on multiple different systems as well.