I have grown weary of being jolted out of bed for no reason by a false alarm. It never happened before we installed the newer, hard-wired-battery-backup smoke detectors that are all connected to each other.
The answer, I hope: apparently arc-fault circuit breakers cause wired smoke detectors to give false positives, and some electricians take those breakers out after inspection (at least on the circuit that is dedicated to the smokes).
I have now replaced the AFCI breaker with a "normal" breaker on the smoke detector circuit.
I posted my question/experiment here: http://ask.metafilter.com/309940/Smoke-Detector-False-Positives-Nuisance-Alarms#inline-4482147
I'll report back in a year.