I wrote a piece for TheFeature about a cool Semantic Web project using PDAs at Carnegie Mellon, called MyCampus.
MyCampus was specifically set up to develop context-aware mobile services for the university's community. The system runs on PDAs and across 700 WLAN access points located around the university, and it is used daily by 3,000 people to help them study, socialize, plan meals, attend events, shop, and engage in extracurricular activities.