Instructables guide on making a twitter mood orb:

http://www.instructables.com/id/Twitter-Mood-Light-The-Worlds-Mood-in-a-Box/ Though the final product looks fairy simple, the backend work looks quite challenging. Making the Arduino search twitter for keywords is difficult because it has to be able to interface with the twitter server. Hooking all of this up requires some backend coding knowledde in php, xml, and some other things.