has an interesting article on the joy of GMail and how it's the harbinger of a whole new way of running applications
But Gmail does work just as well as a copy of Outlook Express running on the desktop. In some way, in fact, it works better. This is big news—bigger, in fact, then most people seem to realize. Until Gmail, practically every Web-based application was a pale imitation of that same application running on a PC. Web-based applications had the advantage that they were accessible from any computer on the Internet on professionally managed servers, that the data was backed up, and that the applications themselves were constantly updated. But compared to applications running on your local machine the web versions had fewer features and performed more slowly. Most users—businesses and consumers alike—were unwilling to make that compromise. Gmail is different. [...] Gmail shows that Web applications with thin clients can have advantages over software running on your desktop. The most obvious is reliability: Gmail runs on Google’s servers, not your hard drive, and Google almost certainly does a better job than you do with routine maintenance, backups, and the like. And because everything is kept on Google’s servers, you don’t have to wait for long downloads. Google’s computers are blazingly fast: searching through the few thousand messages stored in my Gmail account is essentially instantaneous. Searching through the same amount of mail on my local computer takes ten seconds or more.
Having gotten used to GMail now, it's about a million times more efficient that the optional HTML interface for my normal POP mail account, so it may just get promoted to my primary email address when the beta test ends! :)