Pownce (review), the new nanoblogging service that doubles as a person-to-person file transfer product, is often compared to Twitter. Both products enable you to "nanoblog" quick updates on what you're doing. But the products have fundamental and important differences, and if you're curious about which one you should be using, you need to know about them. (Jaiku is also an important product in this space; more on it further down.)
Stick with your friends
The big issue: It has nothing do to with design or features. It's the community. Your community. If you want to use one of these services, use the one your friends are using. Trying to keep up with multiple nanoblog services will drive you insane (I'm tracking several this morning as I write this story, and trying to keep up is nearly destroying my ability to focus). Trying to get friends who are established on one network to join you on a new one is a fool's errand. You might get some to come with you, but there's no doubt that you'll leave others behind.
In Web 2.0 circles, Twitter is the nanoblog service to use. I admit that I say that partly because I have hundreds of followers there and don't want to leave them for another service. Pownce is growing rapidly as people get invitations and try it out, but everyone who leaves Twitter for Pownce is going to be leaving friends behind.
On the other hand, if you're starting from zero, give Pownce a serious look, especially if you're thinking of using it in a work setting. With Pownce, you can easily set up a group of contacts, and use the service to keep co-workers up to date on what you're doing as well as the latest versions of documents you're working on. Also in Pownce, replies to particular nanoblog entries are easily tracked in their own threads, on their own pages. If something you write starts a discussion, it's much easier to keep track of what people are saying than it is on Twitter. Again, this is a great feature for business users.
The practical downside to Pownce, right now, is its lack of support for mobile devices. Twitter works nicely on mobile Web browsers, and also via SMS and IM if you care to use it that way. Twitter is also more open to developers, and there are several services that offer alternative (non-Web-based) interfaces to it. I use Twitteroo. Pownce has a decent desktop client on its own, though.
Pownce and Twitter are not your only options for nanoblogging. Jaiku is also worth exploring. It has several of Pownce's cool features, like discussion tracking, as well as a nice mobile client for Nokia phones. It's also a very useful aggregator of nanoblog feeds. If you feed it the RSS feeds that Pownce and Twitter publish, you can have your own universal nanoblog. For example, here's mine: rafe.jaiku.com. It takes everything I write in Twitter, Pownce, and Webware, as well as my Flickr photos, and puts it all in one place. It doesn't update frequently enough, but it's a powerful service.
And you can't talk about nanoblogging without taking Facebook into account. Facebook lets you track what your friends are doing on your own Facebook page, and thanks to Facebook's new open platform, other services (including Twitter and Pownce) can now update your Facebook feed. There's a good chance Facebook will become even more useful as a social hub as the teams making other apps tweak them to work even better on the Facebook service.
Final note: Dear Meebo people, Can you please add these nanoblog systems to your Web-based instant message aggregator service? Thanks.