1. I'm generally an aisle person because I get up every hour, but in my pre-FT and pre-elite era when I flew domestic coach more short-notice on packed flights when I couldn't board early to be assured overhead space, I would request a middle seat instead of an aisle seat so I'd be sure to have enough room to get my carry-on under the seat in front of me. Some of the aisle seats on some planes have very small under-seat space and by the time you get on the overhead compartments are full of other people's luggage, shopping bags, big Mexican hats, etc., and there may be no room for a back-pack under the aisle seat in front of you. Middle seats in coach almost always have more space than aisle seats, or at least the same amount of space, and sometimes even more space than window seats, and as posted above sitting in a middle seats means you have only one person to disturb to get out, not two.

However, I'm neither real tall nor big, so being compressed on either side wasn't too big a deal balanced against ease of luggage access and getting up.

2. What puzzles me is why some people fuss to sit together (I'm always happy to switch up in F as long as I still have an aisle and it's not bulkhead) and then don't say a word to each other the whole flight. Last week an older Asian businessman (NW PE, by his tag) and his wife were in F, quite separated, perhaps they'd been upgraded last minute The man loudly asked 3 people to switch so he could sit next to the wife, no one was interested, then he asked me (my aisle for his aisle one row up on the opposite side -- no problem -- bonus was I sat next to a charming old gent with many very interesting stories!). The wife stuck her nose in a book and he went to sleep for the rest of the 2-hour flight.

3. If someone refuses to switch, please do NOT demand or even politely ask to know why they won't. Their bladder problems, claustrophobia, or whatever, are their business, and they shouldn't be put on the spot to explain why they won't move (however, it might not hurt to offer them $20 to switch, if they're in coach and refuse )