You're not the only one who has sold the mba and gone back to the ipad 2. However, I can not fathom why people would do this.
I wonder if I'm too old school now, because I do not find a compelling use case for tablets that makes me more productive. Fun, yes. Productive, no. And clearly I value productivity. So that's where I'm coming from.
My argument hinges on the primacy of text input. It's the key to interacting with your computer/tablet. Real buttons, less confusion on my intended actions. Capacitive buttons by Apple are SIGNIFICANTLY better than any others that I have used. Still, I simply can't use the onscreen keyboard for any length of time. I think that a physical keyboard is a necessity, and if the ipad had that, then we're talking a whole new ballgame. But that, to me, is the macbook air 11". Also, I find that I want to prop the ipad up most of the time when interacting with it, rather than holding it with my hand. Again, an 11" air with the keyboard acting as your "base" holds up the screen for you to view it, i.e., when reading or when watching a movie.
The ipad is fun for sure, but when it comes to efficiency, I'd be interested in seeing how much more/less productive a person is when using an ipad and air for identical tasks. I'm not talking about for writing essays. I would bet that even for replying to simple emails using 5 sentences or less, using a real laptop is going to run circles around an ipad.
The ipad is more portable and has longer battery life, but in my opinion, people who are carrying around an ipad + a wireless keyboard aren't really saving as much weight as they think they are. And, I'd say that at 2.39 or whatever pounds or less, there are rapidly diminishing returns on perceived weight and portability. In other words, 2.39 pounds (a macbook air 11) is already so light that the argument that an ipad may have worse text input (virtual keyboard) but so much better portability and battery life justifies its use doesn't fly with me. Because I don't think that the portability of an ipad and an 11" air is markedly different, and that gap shrinks even more when you include people who are using an ipad with a wireless keyboard. Battery life to me is fine because I don't know anyone who can concentrate for more than 5 hours at one time anyway. I'd further argue that doing 5 hours of work on an air would equate to 8 hours on an ipad (wild guess).
I see the argument for having both an air and an ipad. And that argument is this: if you can afford it, then sure, why not? They're not exactly the same device and there are fun things that you can do with a touch interface. But what I'm saying is that if you had to choose one, I can not see why so many are choosing the ipad. I even had an ipad GIVEN to me, and I barely use it. Again, maybe I'm resistant to change or something. But I have found that the early criticism of the tablet market in general is spot on--it's a middle ground that is not ultra mobile and always-in-your-pocket as a smartphone, nor as full-fledged as an ultraportable notebook.