More about productivity, IT, GDP, and growth from the Economist. Blah, blah, blah. I'm really not a big fan of this argument.
From a strategic point of view, it's kind of irrelevant - IT isn't something a firm can ignore, because all it's competitors are investing in it. At the same time, it's rarely the sole mechanism of advantage - for exactly the same reason.
If you really want to read some deep thought about IT and productivity, read Brynjolfsson's work on intangible factors and other complementary inputs.