I think this also varies based on how busy/crowded the coffee shop is. I don't feel too guilty camping when half the tables are empty, but there are many downtown coffee places that are near capacity most of the time.
At any rate, I'm enough of a coffee fiend that I get a new beverage every hour or two anyway. :)
Hogging an entire table with books and a backpack and notes all over is a pet peeve of mine. Especially a larger table that could fit four people being taken up by one person.
Depending on what part of the country you are in, people will share a single small table. I've been places where every open seat is taken and people are sharing, and I've been to places where a person will become confrontational if you ask to share their table - even if it's a four person table!
Another complaint (if I'm allowed to complain about 'free' wifi) is that a lot of places have a slow connection, many AT&T locations seem to be limited to T1 speeds, and the router has bad QoS or bandwidth sharing. So 'that guy' who's streaming YouTube all morning, or updating Windows, or downloading 30 apps from the App store is just ruining the connection for everyone else. Once I tried running 'bundle install' and after 45 minutes, just gave up and went home.
At any rate, I'm enough of a coffee fiend that I get a new beverage every hour or two anyway. :)