Twitter introduce the Follow Button
groups.google.com
groups.google.com
In exactly the same way that Facebook now doesn't have many people signing up, so instead they desperately keep shoving "People you may know!" at you, even though you've never heard of Ima Stalker before.
I do believe, though, that Twitter has lost its way since end 2009 and are largely making stuff up as they go along. It is also fair to assume that they will have pressures to ramp up monetization as they run out of time to bridge the gap between potential and actual revenues. Such is the curse of an insanely high valuation.
EDIT - It seems the flow is a little different. The user doesn't have to connect to the site first; it's just a one-click thing if you're already logged in. Pretty cool, except it seems a little buggy if you have SSL enabled on your Twitter account.
And yes I'm sure there's lots wrong with it. I built a recommendation system, but I stopped hacking on it when I realized that people liked a story more if I lied that their friend shared it. That's what twitter has: social proof.
I also built http://hackerstream.com, so this is a more general problem with my design skills.
I don't have opml import either, but if you mail me your opml I'll set you up with an account (email in profile; let me know what username you want)
You can also use web intents to do things like compose, reply, retweet, or favorite a tweet.