I'm on day 3 of playing unlined fretless, after playing lined for over 8 months. Today I discovered the trick to it, which others have said on TB before but quite frankly I did not understand until now. When I first started on the lined board, it was confusing to me because I saw lines where the frets would be and had to adjust technique and learn to control intonation. When I switched to the unlined board, which has tiny side dots at the major intervals, barely visible in a dimly lit room, I found that trying to map my mental "picture" of the board onto the physical board was confusing and slow. Kept trying to draw the lines in my mind, figure where my fingers should land. However, when I just looked straight ahead and either read a chart or just thought of what I wanted to play in my head, it came immediately to my fingers. That intermediary step of trying to map fingers to the physical board was unneeded and only slowed me down. Ears were just as effective as eyes in keeping me in tune, and aligned on shifts.
This is of course what people have been saying, "just play in the dark." I just didn't understand why until today.
Here's the side view of the board. Dots are not as visible as the camera makes them appear. Sadowsky Metroexpress.