Matt Gemmell has been using the iPad as his only computer for a month.
Most of all, the iPad feels like a tool. The MacBook is much more like a machine, that needs maintenance and expertise. I feel like, on the MacBook, I need to learn how to do something; looking for this configuration, or for that app — monolithic units of capability.
I love this breakdown, as it perfectly sums up something I have tried to vocalize many different ways. In some ways the maintenance is part of the appeal of the Mac (and Windows, for that matter), as that's how you can unleash the full potential of the platform.
"Power users" can tweak and dig into the cool things on a desktop PC, but I would contend that the vast majority of people can do more with an iPad than they can a Mac.