An underappreciated reason for Twitter's success is that the service made it so easy to subscribe to things. Uniform button. One click and you're done. Remember how hard it was before Twitter, with RSS readers? Find feeds, pick feed, view feed, send feed to reader, import feed, pick a folder -- click click clickity click KILL ME ALREADY I GIVE UP.

But Twitter is kind of lame -- centralized, regulated, opaque and brittle. Frustrated users like Dave Winer say it should be supplanted by an open and decentralized system that can't Fail Whale or be pimped out for one company's benefit. That's true, and probably inevitable. But not until we get a "Follow" button that can work on any website and that skips choices only power users care about (feed readers, RSS vs Atom, summary vs full length feed, etc).

Easy following is not a "should" for supplanting Twitter but a must. As Joel Spolsky once wrote, large user bases are built by ruthlessly improving usability:

Whenever you "lower the bar" by even a small amount, making your program, say, 10% easier to use, you dramatically increase the number of people who can use it, say, by 50%."

More usable products, in other words, are more used. For evidence of this look to Tumblr. Like Twitter, Tumblr has a built-in feed  reader and one-click following. This made Tumblr's bloggers quite active; even without a 140-character limit, the company adds five times as many posts as rival WordPress each day, with 1/15th as many users. The feature is so powerful Google's Blogger eventually copied it.

It's going to be tricky, but there's got to be an open way to enable one-click subscriptions outside and across the Twitter, Tumblr and Blogger sandboxes. There's been a big emphasis on the technical aspects of supplanting Twitter, but these user interface details are every bit as important.