Coffee shops are my real office.
I love the vibes. I don't mind the noise since when I'm focused I tune it out anyway. But I like the fact that a) I have to "go somewhere" -- so it's like going to work, and b) I have free refills so $1.95 lasts me a LONG TIME, and c) it's great for people watching when I need to take a break, and d) I get free wifi, and e) I know the staff so well that they give me freebies and also chat up with me when I want to... kind of like a water cooler without being at a real office. I'm mostly a people person, so I really do enjoy the vibes and the atmosphere of having people around.
I tried working at libraries but the quietness freaked me out. I need ambient noise.
As for people looking over my shoulders, etc. -- that's why I pick the corner tables. Also, most people are so busy with their own shit and stuck in their own universes that they're the LEAST interested in what I'm doing.
It's basically an office for me without it being an office (meaning, I'm not stuck there). I can't work at home -- to much distraction (laundry, dishes, TV, bed, household stuff, pets, etc.) I need a routine, and going to and working at a coffee shop fits the bill really well. For me.