As a counterpoint, if you have a backpack, take the right shoulder strap off, and rotate the bag to front while standing, the bag will hang diagonally, not horizontally with the side access flap facing up. You could use your hand to hold it horizontal, but then you don't have two hands to manage the zipper/flap/lens change. As neuro pointed out, back panel access gives you a table to work on.
I have the F-Stop Kenti, and when I swing it round to the side it does hang pretty much horizontal - certainly horizontal enough to be very workable.
It is an extremely comfortable pack not only for long airline terminals but also hiking. I've worn it for hours.
Agreed. I've had mine for two or three years now, and to be honest I've been surprised at how comfortable it is and how long I can wear it without getting tired/sore/annoyed.
The only thing about it that isn't quite perfect is that it's not waterproof, so remember to buy the rain cover with it. (Something I learnt this summer is that the rain cover gets in the way a whole lot less than I thought it would. You can still access your stuff with ease - it stretches enough that you can slip it off the side door without the whole thing coming off.)