Personally, I'd like a tablet that could just be lying on the sofa. It would let me; check something on the net while watching TV, internet banking, read and reply to forums, check email (and do short reply), Skype client, read recipe in the kitchen, control my appleTV, play some 'app' style games. I don't need a full Macbook for this.
I wouldn't see it as a computer replacement in the house and it may be all that is necessary on the road, but as a consumer product not for business. If you need a laptop for business a tablet (as above) would be **** - unless all you need is glorified PDA functionality, ie, email, calender, internet, simple word/excel docs.
I'd buy one, but then again, I have full desktops at home and at work to do the really productive (boring) stuff. The idea of a big ipod touch actually appeals to me.