Plurk is the latest buzz-grabber in the highly competitive revenueless industry of text-ish IM-ish Web 2.0 communication systems. Like Twitter, it's used to post messages. Like Twitter, posts are limited to 140 characters. Unlike Twitter, Plurk's trying too hard to give you things to do.
The beauty of Twitter is its minimalism: You post and you read posts. You could endlessly groom your friend and follow lists, marking favorites and directing messages to get the attention of people cooler than you, but only if that's your thing. The Twitter experience is essentially unchanged whether Twitter's accessed in a web browser, IM client, telephone or third-party application: You post and you read posts.
Plurk is Twitter maximalized, its social implications not only laid bare but automated and tallied on your behalf:
You post and read posts and collect posts and collect friends and form cliques and accumulate karma and fans. Karma is a product of your prolix and socializing skills: The more friends you have, the more you and your friends post, the higher your karma. By generating one innocuous post and connecting to two people, each of whom have posted twice, My profile shows 0.80 karma points and a prominent link about how to accumulate more. In Plurk, each post is a fractional drop in your karmic pool, affecting your ranking regardless of whether you're blithering or entertaining, bad or good.
Posts on Plurk (I really haven't got the nerve to say 'Plurks') are no better or worse than posts on Twitter. Topics orbit around banality: needing coffee, Twitter's downtime, and the need for hookups of any variety. In Twitter, you can be a voyeur and learn how uninteresting everybody else is, which is comforting when your own posts amount to needing coffee, more uptime, and a hookup. In Plork, the dullness is commoditized, and roping more people in increases your karma. It's a messaging service hybridized with strategy gaming and multi-level marketing. Those who type fastest and befriend quickest are profiled on the ironically titled 'Interesting Plurkers' page.
Posts are spread across a timeline, an added layer of presentation that's awfully spiffy but prevents the rapid digestion of updates from my friends. Twitter puts things in a stack: I can get in, see if there's anything important, and get out again. Twitter's stickiness is specifically in its lack of tenacity. I keep going back because there's no effort to make any visit last longer than I want it to. I get to keep up with a couple dozen acquaintances at a very low personal cost.
The timeline doesn't make Plurk better than Twitter either — this is something possible with Twitter data for whomever feels sufficiently motivated. Twitter's popularity and public API has fostered a rich ecology of third-party trackers, standalone applications, visualizers, and rankers. None of them are part of the Twitter UI, and don't impose themselves upon you; you seek 'em out. Twitter can be used as something in service to another goal, while Plurk is firmly oriented around self-aggrandizement and popularity management. It could be used like Twitter, but that's practically working against its design, whereas Twitter is content to sit there with a blank form and your latest messages in a pile. Twitter doesn't have a decapitated dog as its mascot either.