I agree with almost all of your points. Multitasking is great on the Air, however I find the iPad to be great in the field for writing. Battery life is almost endless and it squeezes into a commuter crush way better than any computer. On a tube journey for example I can write and amend manuscripts easily even with one hand: the keyboard is fine unless you are formatting great wadges of text. Also the focus on a single app - often aids my productivity as does not having 3G and being connected to the net ;)
It's a device I would use in public in far more situations than a computer, which I would reserve for static locations: cafés etc. When I do find Wi-fi at either end, a quick sync with Dropbox and I can tidy up and reorder my words in Scrivener on the Air. My only gripes with it are the questionable vertical viewing angle and the paultry (when compared with the iPad's) battery life. If I need to cross reference my information it beats the iPad hands down.
MacBook Air or iPad: Which Should You Buy?