hi All !
nice points Rob. this subject always winds up being like comparing blondes, brunettes and redheads...
this is all a mater of personal preference and more importantly, of confidence.
observation has lead me to believe that the ones who want a 'camo' line are those who hardly if ever watch the line both on in the air and on the water.
those who prefer visible lines watch both as well as the fly.
personally, i go by the (my) logic that if i can't see the line i'm missing out on many possibilities in controlling it, the cast, the drift and the take when using the tip as an indicator, etc, etc, etc.
as Ben so correctly points out, the goal every fly fisher should strive for is to never 'line' a fish or where it may lay, so it shouldn't really be of any importance whatsoever what color the line is
tip: it's very easy to color the line tip with permanent markers. (as long as you don't use a Toluene-based marker that eats up plastic)
that way those who feel the need for discretion can have the best of both worlds...
cheers,
marc