When at home I prefer to plug my laptop into an external monitor, attach an usb mouse and keyboard, and pretend I'm not working off of a laptop.
Works great at first...
However, my laptop monitor keeps turning back on.
I go to System -- Monitor Preferences -- and turn off the laptop screen and it works beautifully. Exactly how I want it to look.
And then spontaneously Ubuntu turns my laptop monitor back on, attaches it to the right of my desktop, and I loose my mouse from time to time...
It is not at any sort of regular interval that I have noticed -- but it happens more than once a day. Have not noticed any regular behavior that causes it.
By loading up Monitor Preferences I can select the laptop monitor and once again turn it off... but I'm getting a little tired of doing so.