Since every MacBook Air review has noted the lack of user-replaceable battery as a negative point, I was just curious: how many current notebook owners actually have an extra battery? I'm not talking about people whose old battery ran out of juice but they still have it laying around, I'm talking about people who have two NEW batteries that they swap back and forth regularly in their notebooks; e.g. for extending battery life on cross-country trips, and so on. I've thought about doing this, but in practical terms, it's a pain. Just keeping both batteries charged would be an exercise in logistics, and a separate charger is expensive -- and yet another item to pack.