Between its superb multiple-monitor support, intelligent programming grouping in the taskbar, Jump Lists, the ever-handy Peek feature, Snap (it works on the desktop, too!), and good ol' Alt-Tab, Windows 8 is the crème de la crème of multitasking--as long as you stay out of the modern UI, that is.
It may not be as gorgeous as OS X's Mission Control, but Windows 8's taskbar-based multitasking is gobs more effective from a workflow standpoint, especially if you have a plethora of programs open. All Windows 8 is missing is virtual-desktop support. (Don't hold your breath.)