The arduino is great for interfacing with sensors, but lacks the horsepower of a PC. One of the projects we are working on is a solar / wind data logger, and I’d like to save the results in a database and be able to graph trends over time. This is best done on the PC. Fortunately, I can write programs on the PC, to interface with the Arduino, in a similar language to the one I use on the Arduino. This language is called Processing. I can also interface with my Apache web server, and use my PHP/MySql abilities to display the results to the rest of the world.