I considered getting a tablet, but all the IT guys I talked to were unanimous that the iPad is for people who want to consume media rather than to produce it. The Air is lighter than the iPad, and I really couldn't be without the real keyboard. The Air's keyboard is identical to my 17 inch, only without the stereo speakers adding en extra two inches on each side.
I have not been disappointed! The Air is worth every penny. The three days on the train were enough to convinced me. The Air sat in my lap for about 1200 miles without ever becoming heavy or uncomfortable...not so the MacPro, which is not only heavy but often extremely hot. Furthermore, coming back from Calgary on the bus the other day, my 17" portable was too big to open all the way between bus seats...I've had the same experience with airplanes. But the Air sits anywhere I can. Even in the private room on the train, I would have had to pull out the table to sit the 17"Pro which then would have been at the wrong angle. The Air was a delight to work with!
The other feature I love is that it is instantly on when you open it. Flash memory means nothing has to spin up to speed or overheat or eat up battery power. I got hours and hours out of my battery. In contrast, the 17" is down to about 90 minutes before it goes down.
Having to get used to Lion operating system though, particularly to the new trackpad motions. I quite like two finger scrolling, once I got used to it, but still find I am accidentally moving my hand without realizing it and triggering all sorts of weird responses...e.g., made a random, accidental circular motion with three fingers and the screen went blurry. It me a couple of minutes to figure out how to redo the motion to refocus the screen. Who knew it could do that?
So 17" will remain my home desktop, moveable but no longer considered portable. The 13" Air will be what I use for trips, presentations, note taking and so on, my true portable. Mary got herself the 11" Air which is even smaller and lighter, but I found the screen bit small for my aging eyes; and I like that the 13 inch is faster and has more memory. So highly recommend the air to writers and editors... Leave iPad for readers.