Ah OK, well for people (like me) who are interested but know nothing about it in detail, Message Queuing Telemetry Transport (MQTT) is a protocol defined by IBM that enables simple, low overhead messaging to be passed around a network and uses publish/subscribe principles for communication. It has been cited as an ideal method for low powered devices (such as arduino) or mobile devices to communicate with a service to get some state information or to publish a device's state. Twitter, Google and other trendy apps use this method already for pushing presence status to a device.
Jonathan Oxer (he of freetronics and SuperHouseTV fame) has indicated he thinks it is the way forward for federated home automation...
To the original poster: I have found the following resources to be interesting to Arduino projectshttp://knolleary.net/arduino-client-for-mqtt/http://blog.m2m.io/post/30048662088/a-simple-example-arduino-mqtt-m2m-io
I hope that is of some help.