I came across this section of an Interstate today:
Notice how the Interstate looks a little like it's been draped across the terrain's ridges and valleys? That's probably because the road was originally traced from non- (or not fully) orthorectified imagery. (From perusing the history of the way's geometry, it looks like the culprit was someone in the US Census Bureau; the waviness was there in the TIGER import.)
I matched the geometry up to Maryland's six-inch imagery (which is, in my experience, excellently aligned and rectified) with this result:
This post is just a reminder that you should be evaluating the qualities of the aerial imagery you use and not just blindly tracing from it.