We just got tipped an email from a reader who emailed Apple VP of Mac Software Engineering Craig Federighi. Cult of Mac reader Stephen Gilbert emailed Federighi about not being able to use fullscreen Mac apps on multiple displays. When you make an app enter fullscreen mode in Lion or Mountain Lion, it will fill one display and blackout your secondary monitor.
For some reason Apple doesn’t allow you to use an app in fullscreen mode while viewing content on another display, and it’s annoying. For instance, entering fullscreen mode for an iTunes movie will make it impossible to use your second display while the video is playing. Not exactly an optimal experience for those who fancy lots of screen real estate..