I left my laptop idling for a few days (waiting for Crashplan to catch up with backups after a hard disk upgrade). When I got back to it, it was running warm. Some investigation in Activity Monitor found an app called Agent Monitor seemed to be the culprit, and further investigation determined it was associated with VTech software (for their bookreaders) I had installed months ago and which, incidentally, never worked.
Uninstall followed by delete. Problem solved.