It is an issue in Windows 7, at least with default settings. As mentioned in the grantparent post, if you have a default taskbar setup (at the bottom, no autohide) you can very easily drag a window below the taskbar (because the taskbar is larger than the entire window titlebar), which might as well be off the screen because the zorder of the taskbar is greater than that of the window, so you can't interact with the window via the mouse until you move the taskbar or set it to auto-hide.