The dot-com bubble? A whole bunch of investment money was poured into businesses operating over the Internet from around the time dial-up became widely available. A few years later, investors realized that "on the Internet" wasn't necessarily the key to making a crapton of money and the stock market crashed. A bunch of companies (many of which never made it to profitability) went under, and a fair number of people lost their jobs. Pets.com was one of the more notable victims.

This doesn't, however, mean that no business is done over the Internet today.