I think 1 and 3 are more interrelated than 2, so we can think about the internet by itself. It seems that the internet has had a profound impact on retailing and price-competition based products (I'm looking at you airlines) by allowing consumers to instantly compare prices without search costs. (Related: I haven't seen "search costs" be mentioned in an economics discussion in several years.) The business to business relationship has been accelerated by the internet, which has been big for inventory management and transactions that require exchanges of large, frequently changing information in a quick period of time.

Impact on the culture of work: High

Benefit to productivity: Low, and primarily concentrated in certain industries

As an accountant, I'm prone to overvalue Excel as a tool. Excel has allowed the "average" business person to manipulate and understand data in quantities that were difficult to imagine a generation ago. But, I think the value of this manipulation is to cheapen the role of data input. That is to say that nearly as much time is spent identifying and correcting errors as in the old days, since correction is so easy in an electronic environment.

Robert McNamara told an anecdote about old-school GM used to put all of its outstanding invoices on a scale and why them to calculate the value of accounts payable at the end of the year. Obviously, Excel allows a great deal more precision in calculating these accounting and finance items, but I think the value of understanding the precise measurement of these amounts is overstated. (Ed: Who knew that by 2010 this acronym would be associated as much with agriculture as cars?)

The biggest dollar value area that Excel has enabled is financial modeling, and look at the fat lot of good that did us.

Too much as been written here for me to add a lot to the discussion. The PC changed everything. However, I think the value of the PC on productivity has been slightly overstated. Computers allow us to more efficiently allocate resources, particularly inventories and manufacturing resources, and the distribution of engineering modeling across computers has changed every industry you can think of. But many of these gains could have been realized under the old mainframe model with better software, in my opinion.

Paul Krugman offhandedly discussed the changes wrought in the economy by computers, specifically, the idea that growth in the economy lagged growth in computer technology by about 20 years. His theory was that business were trying to figure out what to do with computer technology, and ultimately came up with the idea of big box stores. An interesting theory, not without merit.