When you preview an animation, the only way to close the window is the button at the bottom of the screen. (At least in the OS X Version) If your resolution is too small to reach that button due to the fact that that the animation's resolution is high enough to push that part of the window off the screen, there is no way to close the window because you cannot move the window high enough to reach the button (the mac menu bar gets in the way!). Thus, there is no way to get out now other than to force quit, as the close box on the preview does not work.
This is really annoying, and should really be fixed!!! The window bar's close button just needs to close the animation preview window when clicked.