Pretty ballsy stuff Robin. I had a fretless mid 80's that had been de-fretted and maple strips inserted which meant finding the notes was much easier, particularly playing live under a constantly changing light show. Without fret lines it would have been so much harder in the near darkness. If it was my main axe suppose after a while you learn exactly where to be as your ear and bad looks from fellow band mates surely let you know when hitting a bung note.