It's an issue if you take flights that last longer than 3 hours, especially since the battery isn't swappable. And it'll remain so until airlines offer power at every seat, which won't happen soon.
For me, though, the Air's biggest current limitations are the size and/or cost of its HDD and SSD, both of which I hope will be improved later this year.
The last 4 flights I've been on that have been longer than 3 hours have had American and European electrical sockets at the seats. I'm pretty sure the airlines have already thought about this for you. They don't expect people to have traveling gear and extra batteries when they restrict you to such small carry-on bags!