I have been using Twitter for about six weeks and I still cannot give a good account of why.
The description makes it sound like nothing. You type up to a hundred and forty characters. Other people see it. You see theirs. There is no threading, no subject line, no formatting, no way to reply properly, and no obvious purpose. When I explain it to people who do not use it, they wait for the rest of the explanation, and there is no rest.
And yet I check it, and I have stopped checking two feed readers.
The number that gets quoted is the character limit, and it is worth knowing where it comes from, because almost everyone treats it as a philosophy of brevity. It is not. A text message is a hundred and sixty characters. Twitter needs room for a username and a bit of overhead so a message can arrive as an ordinary SMS on an ordinary phone with no software installed. A hundred and forty is what was left after the carriers took their cut.
So the constraint everyone treats as an aesthetic decision is a billing artefact from mobile networks.
What interests me is that the artefact turns out to be the reason the thing works. A hundred and forty characters is too short to make an argument, which means nobody tries. You cannot write a considered position, so you write what you are doing or what you just noticed, and the cost of posting drops to near zero. Blogging never got there. A blog post has a title, and a title implies a thesis, and a thesis implies effort, and so most people with a blog post four times a year and feel guilty in between.
Remove the possibility of saying something substantial and people say small things constantly. The aggregate of the small things turns out to be more interesting than the occasional substantial thing.
I have no idea whether this is a business. There is no advertising, no subscription, and no visible plan. The SMS costs money to send and someone is paying for it. The site falls over regularly, which suggests the infrastructure was built for a side project and is now carrying something else.
Two predictions, neither confident.
The first is that the character limit outlives the reason for it. By the time most people are posting from software rather than SMS, the limit will have stopped being a technical necessity and become the identity of the product, and removing it will be unthinkable.
The second is that this stays small. It requires you to already know people who use it, the value on day one is zero, and the pitch does not survive being explained. I have watched three friends sign up, post twice, and stop.
I am fairly sure about the first one. I would not put much money on the second.