Populist could be one of the more convoluted products I've seen lately, but it's a whole lot of fun once you know what you're doing.
Having recently taken a look at Plurk, I feel compelled to give it a mention here since the two share some quirks in common. Like Plurk, Populist is a service that's been designed to help people broadcast little bits of information to others in a very structured manner. What makes it different is that it's all about stuff you like in various categories like books, movies, TV shows, and more. Jaiku toyed with this idea a little by letting people add tiny icons to their posts, but Populist takes it a step further by making those icons double as categories.
You begin with 14 categories to start filling in. Every time you update that information other folks will be able to view it along with any of your previous entries as noted with a number that shows up when you mouse over it. You can also expand the types of things you're sharing all the way up to 29 categories with some of the more obscure ones like recipes, rides, and "un-obtanium" for things you'll never be able to afford or get your hands on.
Like any other bookmarking service, the idea is that you can find other people who are discovering things you haven't and track what they're digging. In that regard there's a very loosely useful built-in social component that lets you befriend others and track what they're saving and sharing, as well as capture anything they've posted and add it to your own lists.
The only problem is that exploring the existing community is tough. I found the public stream of people's additions a little difficult to sort through (messages are literally flying back and forth across the screen), but once you're on someone's profile it's a simple affair to drill down into any of their categories and find some things worth clicking and potentially bookmarking.
Populist is the first project from the folks at Particle, who include the founder of uber-hip event service Crush3r (review) and the designer of many of Yahoo's mobile apps. Keep an eye on these guys.
See also: Friendfeed