Adam Greenfield has defined ambient informatics as "a state in which information is freely available at the point in space and time someone requires it, generally to support a specific decision." This definition works for me, though I'm maybe a bit more interested in how this information can be used to motivate and influence positive changes in behavior than I am in the perhaps more utilitarian form of simply helping people solve problems or answer questions.
I used this space as a place to keep track of resources while doing some research on ambient informatics as a graduate student at Pratt Institute School of Information and Library Science. Maybe you'll find some of these resources useful as well. The list below is generated from bookmarks available at del.icio.us/dyobmit/ambient-informatics.
You can learn more about me here: timboyd.info