Global Guerrillas posted a link to Tapatio. It looks like it uses twitter to collect and distribute information. It looks like the real value add is that ‘Administrators’ can verify incoming messages and then tag them with metadata before they get republished to the network. It’s a cool idea and it looks like they have even used it in the field. My main worries would be:
No encryption.
Adding tags allows for easy automated interception.
Centralised point of failure (administration).
Dependent on controllable infrastructure (Cell Provider, Internet, Twitter).
Not much value add over existing messaging systems (Twitter, IM, Skype, E-Mail, XMPP, Radio).
Most of those issues could be resolved and are probably on the dev team’s radar.
Check out the rest of their site hackbloc.org for other cool stuff.