I, too, haven't used my iPad since I got my 11" MBA. However, in my case, this is merely the "new-toy" syndrome. I think I'll eventually return to the iPad, probably after iOS 4.2.
They are two different technologies, each with their own advantages:
MBA:
- better for typing large amount of text;
- flash video, and other iTunes non-compatible movies (flv, avi, iso, mkv);
- webcam;
- easier and more flexible vpn; and
- can download zipped files and immediate use/enjoy them.
iPad:
- 3G, GPS
- much easier to use when standing up (on the go);
- longer battery life;
- play (many free) games designed for iPads;
- excellent ebook, e-magazine reader;
- much more ergonomic to your hands/arms for prolonged use;
- need only to carry a USB cable to charge iPad from airplane seats; and
- more (though not entirely) spill-proof, thus more kid-friendly.
This is me, too. I love my new MBA, but I wouldn't give up my iPad: the iPad sits by my chair and goes with me everywhere and is available whenever I think of anything for which I need the internet. I can work with the iPad much more easily in my car (not while driving, ever) than I can with the MBA, for example. The iPad is just so handy. While the MBA is very small, light, and instant on, reaching over and grabbing a device like a laptop makes it less amenable to quickly handling random items that pop into my head. I love both: although they have some overlap, they fill different needs for me. Andy Ihnatko has a good discussion in his review of the MBA as to why the choice is difficult between the iPad and MBA.