I'd recommend dynamic named channels rather than some set of numbers you have to reserve, but I do see the value in having channels.

People should be able to select some set of channels to listen to and be able to direct messages to. The interface might work like this:

/channels
  Active channels:
   General
   Eels
   YAPC Germany
   Badgers vs. Rodents
/mychannels
  You are monitoring:
   0 - General
   1 - YAPC Germany
>1 Würden Sie mich unterrichten, Deutsches zu sprechen?
  <[you]@YAPC Germany> Würden Sie mich unterrichten, Deutsches zu spre
+chen?
>-0
  You are no longer monitoring General
>="My Channel" Hey, I just started this channel.
  Added "My Channel" to list as #0.
  <[you]@My Channel> Hey, I just started this channel.
>+"Eels"
  Added "Eels" to list as #2.
/mychannels
  You are monitoring:
   0 - My Channel
   1 - YAPC Germany
   2 - Eels
/channels
  Active channels:
   General
   Eels
   YAPC Germany
   Badgers vs. Rodents
   My Channel
[download]

Messages that aren't directed to a specific channel would go to your channel 0.