I just installed Ubuntu 12.10 (I formatted my old Lucid Lynx drive by accident). It's been working great, but every now and then (especially when I leave) this pops up, lasts for about 5 seconds, fades away, and a new one appears. I am using a Dell Studio 1737, a USB HDD for Ubuntu, a USB mouse and a USB keyboard. It's always plugged in, too, if that helps.
I've googled around, and I've seen a post that lead me to believe that my problem is related to the media hotkeys on the built-in keyboard. They look like this.
It seems that a log-out CAN fix it. Sometimes I have to restart, or shutdown and hard boot.
My friend thinks that it's a driver problem.
I've had good experiences with Ubuntu, left for Windows because of gaming, and I came back because of Steam. I'm very disappointed in the downgrade from Lucid Lynx to Quantal Quetzal.
I hope someone can make this an upgrade for me.