For our project we wanted to create an Ethernet data logger that could take data from a temperature sensor and a PIR motion sensor. This would allow us to graph motion and temperature over time allowing users to know when a space was most in use and perhaps whether it was being heated effectively.
See example website
Arduino– The Arduino here connects collects the temperature data and movement data to the Internet as a client and posts data to the Google App Engine site every 60 seconds. An external interrupt allows for motion to be detected and polled at any time. The temperature is read just before the HTTP post is made.
Google App Engine – On this side the app engine takes the data posted from the Arduino and stores it in a simple / and probably inefficient database. If someone visits the site it uses the google graph api to make a pretty neat graph of the data over time.