Having just received one as a generous and unexpected gift (witness previous entry), I’m trying to puzzle that out for myself.
It’s significantly bulkier and heavier than my Slingshot Organizer or the scraps of paper I write shopping lists on, so I cannot see it replacing either.
It’s also significantly heavier than my paper journal book, though it ties it in bulk. However, typing on a “keyboard” that appears on a touch screen is every bit as slow and error-prone as it always seemed to me it would be, so it’s of limited utility as a journal-entering device. A keyboard would rectify this (and they are available), but then the result would be both heavier and bulkier than what it replaces.
It’s also much heavier and bulkier than my MP3 player, and it’s an awkward form factor to use as a camera.
That leaves a device suited primarily to the consumption of information in digital form, be it in the form of Web pages or e-books, one which can be pressed into service for entering text if that need should arise. It is definitely less heavy and bulky than the alternative of a laptop computer.
If you purchase an adapter, it also possible to download images from a digital camera into an iPad. The same advantages of less weight and bulk (compared to a laptop) apply in this case, too.
So, it’s a nice gift that will at times come in handy, but I also don’t expect to be carrying it with me routinely; the things it does better than the existing alternatives tend not to be things I do all that frequently away from home.