There seems to be more buzz and attention now about Twitter now that the in-crowd is using it more to post their thoughts, so I've turned it back on in my IM and will start using it a bit more. But I'm hesitant to start relying on some hosted service like that... like my blog and IM, I'd rather have it hosted myself, under my ownership.
Twitter's sort of interesting as I was both right and wrong in my thoughts about it when it launched. I was asked my opinion about it back when I was at Yahoo! and I was generally positive - I viewed Twitter as a mobile group chat and IM-echobot and since these were things I had been playing with and pushing for Y! to implement, I was confident in their success. However I was *convinced* that Twitter was going to have to implement channels or rooms at some point because of all the cross-chatter in the initial release. I was positive it wasn't going to be able to scale as it was, and I was semi-right, but with only some minor improvements (the @user system) it seems to be working just fine.
Twitter's insistence on simplicity is actually admirable and has served them well, I would have tweaked it more. In 20/20 hindsight, making everyone's posts be public initially made sure that they were able to get past that beginning phase of a social network where no one has enough friends to make it worthwhile. Twitter was able to gain critical mass by forcing everyone in the same room, more or less.
Compare this to Jaiku which has much of the same functionality as Twitter, but also has dedicated IRC-like channels as well. Lots of those channels have been created but are now dead... I ran into one I created the other day for the Mobile 2.0 conference in October, it still existed even though it had long out-lived its usefulness. I've seen some effort to mark Twitter messages with hashed #tags to act like rooms and this is a fantastic idea (something I've played with as well). There's a vast gap between an explicit "channel" and the implicit "tag" with the latter being much more flexible and dynamic. One demands that there be activity in a room or channel, as being the only person in a room is lonely, but using tags is more like graffiti left on a wall by passing travelers. Regardless, like I said, Twitter is working quite well without a channel implementation at all.
So if Twitter is essentially just a big chat room, what about the other "micro-blogging" services, and stuff like "regular" blogging, Pownce, Tumblr and even Facebook's Status messages? To me it seems pretty simple: Services are either focused on the messages themselves, or they're focused on something else, and messages are ancillary. This is somewhat fuzzy because of how much stuff looks like a message: I mean, ever notice how much different sorts of info fit really well into an RSS/Atom feed? That's because so much stuff can be boiled down to simply a creation date, a title and some content.
Facebook status messages aren't a competitor to Twitter, for example. Facebook would probably work just as well without them, and much of the the other messaging stuff, as long as the general activity stream was kept, as well as the ability to add/remove friends, browse profiles and pictures was kept intact.
Taking messaging out of Twitter or Jaiku, however, wouldn't work. It seems like a no brainer to say that, but consider regular blogs as well. It also wouldn't work to take the "messages" - i.e. posts - out of blogs either, would it? We'd be left with Personal Home Pages again. Once you get that in your head, you can see the core essence of various services, I think. Tumbleblogs are like Twitters, but without the social networking. Blogs are long-form public messages, emails are long-form private messages. IM is one-to-one short-form private messages, IRC are short form public messages, and so on. Add something in like File Sharing and you get Pownce. Take something out - like the ability to use a website at all or titles, and you get SMS. You get the idea.
The great thing about "messages" is that they're free-form. You can pull and push them all over the place, organize them how you want, tag and categorize them, etc. The problem I see is that all the other stuff has to be centralized somehow - users need to be identified, relationships need to be confirmed and then tracked, privacy needs to be ensured, etc. There's no good way to wrap any of that around a message in a portable way just yet.
And that, in the end, is why I'm hesitant to start using Twitter or any other service like that. It's not the messaging itself or the style or usefulness of it that bothers me, its having to rely on all those other services which I know aren't portable or under my control. I guess it's an old-school way of looking at online services, and not very Web 2.0 of me, I know, but I can't seem to help it.