Because I need my laptop at home, so can't lock it up at work. And I need it at work, so I can't leave it at home.

I don't need the data. I need the LCD, the keyboard, the operating system, and all the stuff that goes with it. Some of us actually need it both places. If you wish to donate $1700 to buy me a MacBook Air, I suppose I could leave that locked up at work and leave my Black MacBook here at home, and take my 250GB external around between them. Until that happens, I'm lugging the lappie around, just like I have since Sept. '06 when I started. 5,000 miles of commuting with a laptop and I have yet to break anything.