I am typing this on my Lenovo X61 tablet running Windows
Vista. I use the tablet functionality 10% of the time. The tablet features are handy in my classroom, where it, in conjunction with a data projector, replaces an overhead projector. And I write solutions to math and physics problems directly onto the screen, and then post them to my web site as gif files. But if I were not a teacher, I would never use this as a tablet.
Tablets are, of course, great for visual artists who want to use digital media.
I won't be lining up for Apple's tablet. It has no serious apps that interest me, and it will be too expensive as a toy.
edit: This rumour has been around for a long time. I'll believe it when I see it.