We just returned from a charter in Maine that exposed a problem for boats without automatic identification system capabilities, or even for boats with AIS.
One day we were sailing the chartered Baba 35 from Boothbay Harbor, headed to Tenants Harbor, and were close to Mosquito Island when a thick fog came in, limiting visibility to about 100 to 200 feet. Since the previous two days had bad weather and fog, there was a lot of sail- and powerboat traffic in each direction, including a number of New York Yacht Club cruising boats. We turned on our radar only to find out from the chatter on the VHF that a lot of boats seemed to be more focused on their AIS and whether they were being seen by each other than looking at their radar or posting a lookout on the foredeck. It appeared that many no longer used radar reflectors, judging from their small profiles on my radar. Their speed and near collisions led me to believe that they were overtrusting AIS. I suppose at some point everyone will have AIS, but until then, it is almost more risky than ever in the coastal areas in fog.