A week ago, I ceremoniously yanked out my MacBook's Ethernet cable and toggled off the Wi-Fi. Once I was positive the machine was cut off from the Internet, I added a task to my online to-do list. It worked. I sat back and smiled, agog—I had just seen the future of software.

I wrangle my to-dos with a Web service called Remember the Milk. Compared with a bloated behemoth like Outlook, it's a streamlined, fun-to-use wonder. Rather than sitting on one PC's hard disk, RTM lives on the Web, where it's available on every computer I use. Up until that day, though, it had the same overwhelming problem as every other Net-based service on the planet: It was ... well, Net-based. No Internet connection, no to-do list.