I had some issues with my wireless at my school. I had tried everything almost and usually it did not want to connect, or when it connected, it disconnected again a few minutes later.
Someone suggested that I could install Windows Wireless drivers. I did that and had better luck connecting, but still disconnection issues.
Then someone suggested wicd. I install that and after I did that, wlan0 disappeared. I could not connect in any way with wicd and even after uninstalling it and installing network-manager again, it is still not there. (and countless reboots).
I have tried adding
auto wlan0 inet dhcp
To interfaces but nothing works. The wired connection still works fine.