--- This question is related to Ubuntu 12.10, since previous versions did not connect to network before login ---
I had a bad boot today: the Ubuntu screen was blocked at startup time, after a green [OK] and a white blinking underscore. In recovery mode I figured out the problem: NetworkManager hung trying to connect to a wireless network that wasn't available anymore, and so I couldn't reach the prelogin level.
Anyway: I really don't like that the pc connects to a network before the user logging in. How is it possible to disable it?