Holy crap. Every week there's a miniature gold rush when a new microblogging site is released. Twitter proved the market, and the concept is so simple that anyone with an elementary web development education can put up their own site. And, apparently they are.
So, Twitter kicked the whole thing off, and it's a compelling system because it's incredibly simple, and very accessible (web, IM, widgets, SMS, etc). It's also pretty flakey right now. More on that later.
Immediately after Twitter's user base "hockey sticked," Pownce and Jaiku jumped on the scene, with a couple extra features, like pulling in photos from Flickr and whatnot. [ed: turns out Jaiku launched a few months before Twitter, my bad]
FriendFeed joined the fray at around the same time, adding a veritable raft load of ways to track and comment on posts from other sites.
Then Plurk leaped into battle with it's headless Doglephant and wildly different user interface, provoking Love It or Hate It responses from everyone who tried it. They don't pull in other content, but they do allow discussions to grow around specific messages, and they added the concept of karma -- more participation means more karma, and extra little toys to play with.
This week, Identi.ca showed up with a back to basics story, and a twist. It's pretty much just like Twitter, and people want to give it a shot because it seems to be more reliable (more on that later). The twist is basically a marketing move: the software that powers the Identi.ca site is an open source project, so anyone with software chops can use it to create their own micro-blogging community. Heads up, internal communications people.
Now, regarding reliability. A slightly flakey experience is not a big enough factor to drive away the masses. None of the above sites are Twitter killers, because Twitter has a critical mass of users who have shown that even if Twitter is unreliable, they'll stick it out to stay in touch with their friends. Will it frustrate early adopters with short attention spans, and rabid interaction habits? Sure. Will they totally abandon Twitter? Not likely.
My prediction? Twitter is going to stay king of the microblogging universe for the next few years, and that universe is going to get much, much bigger. Like Gary Vaynerchuk said on his swing through Portland -- "You think there's a lot of people using Twitter now? Wait until Oprah gets on Twitter." Hopefully, the fine folks at Twitter are planning for such an event.
I expect that we short attention span, early adopter types are going to stick with Twitter, but spend most of our time on FriendFeed. Why? Because it's such a powerful aggregator. We'll continue to sign up for any social web app that shows up on the radar, and we'll use FriendFeed to track and manage all of our discussions.