Do you like maps? In Amsterdam they've hooked GPS's to volunteers and are mapping the city based on the collected traces. Too cool.
In between working on C++ code at work I've been putting together PHP code to load weather readings into a mySQL database (fired off by a cron job) and some PHP routines for turning the accrued data into meaningful graphs. The goal is to replace the images on our weather page. Currently they are produced by a program called VWS, running on a home pc and uploaded regularly. That's a bunch of large uploads, which aren't viewed all that often. So now the data scripts are grinding, the graphing scripts are plotting, and it's just a matter of getting a few more weeks of readings into the database to have some fun.
Sure, computers are fine for *serious* work but isn't the best thrill from finding a new game or an awesome screensaver? Marc Liyanage, always a great source for the latest OSX packages (PHP, MySQL, Apache, etc...) now has a whole page dedicated to customizing OS X including a link to the Solar Winds screensaver. My favorite setting is Cold Pricklies, but Cosmic Strings and Space Fur are a close second.