I would tend to agree with jdCaptivate's take on to screen traces on most phones. Some people are more OCD than others and will constantly wipe and clean while most will do it only occasionally. I keep my screen somewhere in the middle and yes, I can see the path I use most often when looking at the right angle. If I used a pattern lock someone could most likely see that path as well.
Blessed are they who can laugh at themselves, for they shall never cease to be amused.