Hal Varian on why it might really be (sort of) Different This Time:
Think back to those railroad tracks. The only thing one could do with those railroad tracks was carry trains. It would have been fantastic if the miles of excess railroad tracks could have been transformed into highways to service the new growth industry coming on in the next decade: the automobile.
But today, if you have fiber you can carry voice, data, audio, video, transactions, whatever. You can set up a database for MP3 recordings, and it's not so hard to repurpose that to handle supermarket transactions if the MP3 business doesn't pan out. Communication technology and information technology can often be transformed reasonably quickly to support other innovative activities.
That's a prime capability of computers. It means you're less likely to end up with an oversupply in the classic sense, which we saw in these other historical periods. The technology boom and bust cycle isn't eliminated, but it will have less of an effect than in prior decades.