Most discussions talk about GMail as just another web-based free e-mail address that happens to have 1G of storage. But that isn't it at all.
GMail asks and answers the question, "What e-mail client would you build if you never had to delete any of your old e-mail?" GMail is designed to organize your information for easy access later. Messages are threaded, part of a conversation on a topic. Searching your mail is emphasized. And, because it's web-based, you can access you mail and any information in your mail from any computer. The 1G of storage is just a means to the end.