Uses for an iPad or other tablet...
Commuting - excellent for catching up with your email, diary, browsing the intarwebs, listening to music or podcast, reading a book, whilst sitting or standing on a train/bus/plane.
Reading in bed. Excellent device that doesn't need the light on (thus not disturbing my partner). Also listening to the iPlayer, podcasts, etc. (much better sound quality from the built-in speaker than an iPhone). The screen's much bigger than a phone, so it's easier to read without my glasses.
Lightweight browsing in front of the telly, in the kitchen, on the bog...
Excellent mapping applications for use as a GPS substitute in a car.
Excellent charting applications when sailing (a tenth of the price of normal charts).
Playing the odd game - nothing like flinging a few birds at pigs.
In short it's an excellent consumer of information that's an excellent form factor - no keyboard, instant on, portrait format screen, etc.
It's not as good as the normal laptop/desktop when using it for serious browsing, development, writing, drawing.... All the sorts of things you'd use your ultra-portable for (but not in portrait format).
I'm absolutely delighted with my iPad and use it daily ever since I got it last May.