identi.ca is a microblogging free service (Affero-GPL) that allows a quick and short communication and is relatively non-intrusive. There is quite a few that it exists, but on the recent UDS, Ubuntu Developers Summit, in Barcelona for a whole week, it was extensively used.
As quite a few ubuntaires used threre, Àlex Muntada created the group ubuntaires for an internal fluid communication. The system is perhaps more informal that writing on a blog and that makes it appealing.
In order to read and write on this group, you must register on identi.ca and subscribe to the ubuntaires group. For a message on the group (related with Ubuntu, of course), only must be added !ubuntaires. Think that only have 140 characters to express yourselves. And that we speak mainly in Catalan. 🙂