I realised today what twitter almost is - but isn't.
It's almost IRC.
The scenario I envisaged today: at LCA this year, there were many IRC channels in use: the main #linux.conf.au, but also many #lca2007-mata for the Mathews A room.
If twitter had channels that one could subscribe too, it would make a wonderful extension/replacement for this kind of thing. Participants could keep up to date with the channel via IM (the Jabber client exists already), email, web - or via SMS.
Scoble has already had almost this experience. It could be done now - but it would require every participant to follow every other participant, and then they'd see every message from all those people. There'd be a constant "Add me too!" and another 700 people have to go follow that one more person.. it'd be insane!
I'd like to just be able to "/j #lca2007", and see all the messages sent to that channel - but only messages sent to that channel, not the ones about the participants personal lives as well.
I can think of quite a few revenue models here:
* Subscription service with fixed amount of SMS per month
* Charge events such as LCA a nominal fee to get the channel set up - such a fee could be included in registration fees (or paid for by sponsorship). I don't think this is such a crazy idea: the organisers of the conference would surely love a broadcast service that allowed them to advise attendees of venue changes, make announcements, etc
* The Adsense model - you can join #lca2007 for free, but every 10th message you receive will be a targeted advertisement. This blends with the other two ideas of course - the ads could be from event sponsors, from people who want to advertise at the event (I'm thinking of events like Comdex - how much would companies pay to have an opt-in advertising avenue like that?) - and of course, there could be a subscription fee to get rid of the ads.
Twitterheads, get cracking! Channels, please!
 I like scoble's syntax for directing messages to a person, would be well modified to send to a group - just start a message with "@lca2007" to send to the lca2007 channel.
Update: I'm not the first to have made the IRC connection. 200ok mentions the similarity, but doesn't suggest channels. Teamforce suggests using IRC rather than twitter - but it seems to me that this is solely because twitter doesn't have channels. CruelToBeKind has even more reasons for Twitter to implement IRC-like channels.
Please, twitter - Channels, please!