I've updated to version 1970 and command-tab doesn't work when the VM window is in focus. I'm running WinXP in a VM and I know that Parallels Tools is running because the mouse is behaving as expected. I see the warning that the version of Tools that I'm using isn't up to date that other people have reported, so I wonder if this is related. I have verified in Windows that I'm using the 1970 version of Tools. Here's what I see... If I'm not if full screen mode and I click the top of the VM window, but not inside it, I can command-tab over to a different application as expected. If I click inside the VM window command-tab no longer works. If I make the VM full-screen, I can't command-tab over to a different app -- I have to bring the VM out of full screen mode and click outside the window for the command key to work again. Very cumbersome.
I certainly wouldn't mind an option to have the behavior you are asking for, but the behavior you are describing is EXACTLY what I want.