It's still pretty pervasive in the marine industry, however most of the time the letters don't matter so much as what they mean. I've forgotten half of the alphabet, and definitely couldn't translate a sentence from the flashing light the way I was trained to, but I encounter at least one of the various single letter codes just about every day on the water.

Racons (radar beacons) transmit an identifying letter that appears on our radar, letting us visually identify important points of land. For example I can easily distinguish the entrance to the Fraser River from the sandflats at Robert's Bank because they have different letters.

Flashing morse A lights are used on fairway buoys to mark safe water.

Flashing morse U lights are used on oil rigs to signal a danger.

Morse O is the emergency signal for a man overboard. Every crew member knows where to go and what to do immediately upon hearing that signal.

Different morse sound signals can be used to indicate you're turning to port, starboard, overtaking a vessel, moving astern, or concerned about what the other vessel is doing - given the prevalence of radios only the last two seem to be used regularly, but if someone wasn't responding on radio it gives me a way of letting the other ship know what I'm about to do.

Similarly, others are used as fog signals to indicate what type of vessel you are and what your status is (for example I can tell a normal power driven vessel from a tugboat or vessel restricted in its ability to manoeuver).

And as the aviation guy mentioned, we've got some aviation electronics on board transmits our identification code when we're doing helicopter operations as a backup to help them find us.