Maybe I should stop reading those forums postsI had just convinced myself to go for the 13" Air and now I read some very good reasons to go for a rMBP 15" (I really loved the screen when I visited a Mac reseller yesterday)
I want to buy a Macbook (Air 13" or retina 15") before august. So I can start working on a Mac (Wineskin) version of my software. Because of this I can not wait for a Haswell update in october (if they update the 15" Retina within 14 days after I bought it, I will return it for a newer version)
Now I'm thinking again to get a 15" retina instead of the Air. But it is still a shame to spend that amount of money on a system that will be updated very soon. But maybe that is the story of all computer buyers...
Getting 6 hours is still nice, I just should not forget to take the adapter with me on my weekly travels (by train 4 hours).
If you want to save some weight on commuting, buy a second Air power supply; it is smaller that the one from the rMBP and will also charge your machine (my wife has a 2012 air and have tried it, will take longer to charge, of course)