Interesting post!
The last two occassions I have been flying (last weekend going to and coming from the Qantas B707 VH-X(E)BA "City of Canberra" arrival at YLRE) there have been beacons going off on 121.5. One around Proserpine and one around Townsville. Never heard anymore about them in relation to either aircraft or boats - so I assume they were false alarms.
When I was in NZ (20+ yrs ago) there was a spate of false beacon alerts. All pilots were sent a letter by the Civi Aviation Department (or whatever they were called), to check before shutting down that our beacon had not activated, and we were threatened with dire consequences for false activations.
Only a matter of weeks later there was a major search in the Wellington area (involving helicopters and all) for a beacon that was going off. It was eventually located in a cupboard in the Civil Aviation Department's Head Office. We got good mileage out of that for some time afterwards!
Dr