What's the Apple iPad's Killer App?

I'm no Apple fanboy, but seeing Steve Jobs on stage in person is exciting, and it isn't just about his personal magnetism. Apple has $29 billion in the bank and Steve seems determined to spend it building really cool stuff. The iPad certainly fits that bill. Just a little slab of a display lets you play games, browse the Web, watch movies, view pictures, read eBooks, get directions, send e-mail, manage your calendar, and, well, anything else developers want to write applications to do. But after the ridiculously hyped build up and the dramatic launch event, I'm still not sure what most people will use it for. What's the iPad's killer app?

Jobs positions the iPad explicitly as the “middle thing" between a laptop and a smartphone. “More intimate than a laptop, more capable than a smartphone," was his key quote and it is a good one. The problem is, the basements of early adopters across the country are packed with products that tried to be this “middle thing." No one used them. Smartbooks haven't even arrived and no one wants one. Palm Folio anyone?

Most of us already carry a laptop and smartphone. I don't think the iPad will replace either one. I know Steve wants the iPad to slide neatly between the two, but I'm getting on a plane tomorrow and my bag is already hurting my back. I can't carry more. So, again, what is the iPad for?