iTunes 11 Mini Player disappeared off screen
After a couple of minutes of trying, I got the window back. Since I couldn't find this solution on Google, I'm answering it here for other people if they run into the same issue.

To get the Mini Player window back if it's off screen, use the iTunes View &gt; Show Up Next menu entry. In my case, it moved the Mini Player window to a location right beneath the OS X menu bar and displayed the Up Next list, allowing me to move the Mini Player to a location of my choice.