Or you could just have a laptop and take the whole thing with you.
I can name one thing a tablet can do that a conventional notebook can't.
Hold it stably in one hand while using it with the other.
Standard form factor notebooks are unwieldy at best and pretty much have to be set down on something to even be decently usable. Sure, you
can hold it in one hand, but the risk is very high that it will tip out of your hand and fall while you're using it. This is one of the reasons I've been waiting for a tablet and why I like my iPhone 3G so much--I can use it almost anywhere.
Now, for something almost 6x the size of an iPhone, we may have the true use of a tablet; something you can use comfortably with one hand and can serve almost any purpose for which a clipboard was so ubiquitous historically. PnP gamers can use it for their rule books and character sheets; doctors can use it for patient data, lawyers can use it for client data and possibly even heavy research... I mean, the thing is almost unlimited in use, even if it isn't a full desktop processor as so many seem to want from it.
Can it play the latest and greatest games? I doubt it. Can it do the heavy Photoshop or Final Cut processing? I doubt it. But if it can handle the everyday stuff--if it can do things like iPhoto and iMovie, or play some of the lesser handheld games similar to the Nintendo DS or Sony PSP, then maybe it's a worthwhile product, hmmm?