This may be useful for people using the Arduino Ethernet shield to connect to the web - I've just uploaded two examples using www.pachube.com
(a) to give your Arduino "remote" sensors and to share your realtime sensor data with others (and graph, store and monitor remotely); and (b) to use a web page to control the Arduino remotely (this requires no additional server-side programming, it's just an HTML page).
Arduino Ethernet and Pachube: remote sensors & web-control: http://community.pachube.com/?q=node/112
These sketches should make Arduino-based web-controlled home automation, and remote-responsive spaces a lot easier. The advantage of working with an ethernet shield is that you no longer need to tether the Arduino to a computer in order to access Pachube and other network services!
These are coded for the official Arduino Ethernet shield. We've had better, more consistent, results with this shield than others that are available; we also find it easier to work with and code for so we'll generally be developing examples using this shield from now.
(The web-accessing code could be edited to connect to any web service; the advantage is that it repeatedly connects to a website on a given interval, and between connections keeps looping normally so that the sketch doesn't freeze)