In 2004, people paid over $150 on eBay for an email address. Google launched Gmail on April 1, 2004, and most people assumed it was an April Fools' joke. It offered a full gigabyte of free storage at a time when Hotmail gave you 2MB. The catch was that you couldn't just sign up. You needed an invite, and Google handed out only a small number of them. So people did what people do and took it to eBay. Gmail invites started selling for real money. Some sellers swapped them for concert tickets,…