Apple kind of deprived people who use a Dual Screen setup.
When you use an application in Full Screen mode, the second screen gets the grey linen background automatically and you can't use it whatsoever (except for moving your mouse cursor there, (yet?)), kind of bumps me out, because I really like both using a Dual Screen setup and full screen apps.
They should've allowed users to run two apps in full screen side-by-side if you have a dual screen setup, or have some kind of use for the second screen for the same app (for example, have two tabs side-by-side in Safari, have the next month/week/day in iCal on the second screen etc).