I have the 17 inch and take it everywhere (its still new so it has not been on a plane yet, but soon will be later this month, so i'll let you know after that) but I have not had a problem with it, and I am glad I went with the 17 inch because i never run out of screen space.
I know people hate to hear this, but this is such a question of personal preference.
I've used notebooks from as little as 11" and up to 17". For me, the 15" is the biggest I would go, and will be my next purchase. I do like to put the computer on lap occasionally as well as picking it up and moving it around the house, office, etc. It really depends on how much mobility you want.
I think a 17" notebook is really intended to be a desktop substitute, for someone who can not afford being anchored to one. A 15" is just so much more versatile... again personal preference.