Recently I was thinking about them, after becoming aware of the wind noise in my ears. Then I tried a few experiments:
-If you turn your head 90 degrees to one side, the noise goes way down. This is not practical for very long...
-Covering the ears with ear warmers doesn't help noticeably
-Cupping your hand in the vicinity of the ear helps a bit in certain positions.
-Removing your helmet helps A LOT! It's almost as effective as turning the head 90 degrees.
-Using a fabric helmet cover did not make a noticeable difference.
The reduction in wind noise when not wearing a helmet was surprising. It appears that there must be quite a bit of turbulence around the edge of the helmet. It would be interesting to try a time-trial helmet to see if it is any quieter.
PS: the ear cover gadgets have been re-invented. They look very much like what I remember seeing years ago: