Excellent poll question and something I was already thinking about.  I'm the one vote for avoid them at all costs. A few days ago someone posted a video showing a guy playing  the Star Wars theme, (I think.)  Fiddlerman said that one should never hold the violin the way this fellow did, with his chin in a position that allowed him to look straight down the violin neck.  Looking at the video, it was apparent that the reason he was doing this was that he had stickies on the neck of his violin that he was using as visual position queues. I did some thinking about that, since I too was trying to visually see where to put my fingers to play notes, albeit without the stickies -- and missing as often as not by 10-15 cents.  So I decided to try to play without looking at the neck at all, just to see what would happen. Surprisingly, my intonation improved almost immediately, and when my fingers missed the mark, they immediately adjusted themselves to the correct pitch without my looking at the neck at all.

While I realize that visual queues may be somewhat helpful in violin playing, it seems that one might be better off by "seeing" with one's ears more than one's eyes.  For the piano or guitar, visual locations are very helpful because you either hit the key; put your finger behind the right fret, or you don't. The visual queues there are easy to see and the targets are pretty large. With the violin, missing by a couple of millimeters makes a noticeable difference in pitch and you just can't see that small a target accurately enough with tape or without. I'm becoming convinced that tactile landmarks like the base of the scroll or your hand touching the upper bout, as well as the feel of how far your fingers are spread (muscle memory), combined with really listening to the pitch is the key to success on fretless instruments.  I say toss the tape.