My girlfriend is ready to set aside her Macbook for one of these. While I could never do that she does not use her Macbook for a fraction of what I use mine for. So I could see a bunch of people who are casual users making the switch.
I know there will be one in our household. Nothing could be better in some situations. Imagine watching the ballgame, seeing a commercial for productx and grabbing the iPad off the coffee table so you can look it up on the web really quick.
Of course I would prefer an Android tablet, but I know the wife will prefer the sleek design and ease of use of the iPad. Hell as everyone says - it's an iPod on steroids. She (like a bajillion others) loves her iPod, knows how to use her iPod and that makes her want this even more.
The next Android tablet in production needs to have a long hard look at this thing. Hell Android in general does. To reach the masses, make it look good, make a foolproof UI, and make it connect and communicate with your home computer without the command line. Android doesn't need to attract us. We're geeky smartphone people.
I could see plenty of reasons why I would want one. Yes, as a sofa internet tablet while watching TV; also as a casual eBook reader. To buy one of these for taking on vacation or weekend trips with the optional camera connection kit would make me far happier than schlepping my MacBook! And I'm sure that my Doctor, who carries an HP notebook with him all day long, would rather have a simple tablet app on an iPad instead.
I think this has potential to be bigger than just a computer for non-computer users. With a few changes I could see myself getting an ipad (and a lot of other people). At my job I have to print out tons of reports (as I'm sure many people do too) every week. I also have some reports that are too big to print. With the ipad I could put all the reports into this one device which I could take to meetings. This would give me access to all of my reports from the last year, two years, etc (which I obviously couldn't do with printed pages since that would be too many pages). In addition, I could have access to those super huge reports that are too big to print. And the best part is that since they would be in "numbers" I could search them, move stuff around by touching and dragging, hightlight things, etc.
The things that will stop me from pulling the trigger- No multi-tasking. So if I'm looking at a report and want to take notes at a meeting I'd have to close the report open the notes app, then close the notes app and go back to the report. I couldn't have a report open and a note taking window layered on top like on a laptop. The other issue, is that I would never take notes on this thing with the on-screen keyboard. I'd need a pen of some sort since it's just faster and easier. Now I know I could get a pogo pen or whatever that is, but I'm still not sold that the ipad will be all that. If it could do these things I think this could be a hit in some businesses and definitely in the education field (colleges, etc).
There are also a bunch of similar devices coming out. The notion ink tablet seems pretty ridiculous too...