I don't know about "classic tests", but I've successfully written fully-functional scripts while having a phone conversation, browsing HN and chatting on IM. You just have to set priorities. You obviously can't read something in as much depth, but it's great for reading for filtering out good stuff to read in more depth later.
I wonder how much money is being lost by businesses who buy multiple monitors for their employees and "allow" or encourage them to multitask?
I'm not sure that multiple monitors is about multitasking - you can only physically focus your eyes on a limited amount of screen; peripheral vision allows for more I guess. Multiple monitors (I've only ever used 1 or 2) just make task switching easier but I didn't find 2 monitors any better (more productive, more convenient) than simply using multiple screens in KDE.
I would argue that most "self proclaimed" anything aren't as good at their trade as they think.