Tip of the Hat: Reddit
The main problem with good UI design is that it’s transparent. People don’t notice the good stuff—they just focus on the thirty things that are broken.
But what’s rather charming is that when you view reddit, the links you’ve already visited are displayed in purple. You know, that webbrowser standard for a followed link. Even if you’re on a different PC. It’s such a nice touch—Links that I viewed at home this morning are purpled-out when I’m at my desk at work. And I didn’t have to learn anything—it so snuggly fitted my mental model for How The Web Works that it took me a few weeks to notice.
Compare that to digg where even on the same PC, I can’t eyeball the page and see new links.
Nice work, reddit-folk!