I always use a proxy to connect to the internet in Windows as well as in previous versions of Ubuntu, but in Ubuntu 11.10 it seems that the proxy settings I set in the GUI are not being applied system-wide.
I can access the internet in Firefox with its own proxy settings. I can access internet in the terminal (i.e. I am able to use apt-get for some small programs). But in Ubuntu software centre or update manager it is not working.