I wrote previously on how Shape2Earth can now create center-points from polygons that can be used for labeling. The next thing I need to do is create the same functionality for lines. This is a bit trickier than for polygons. Imagine using the bounding envelope for the Missouri River to create a center-point to label the River. Its just not going to be in a very effective place.
The idea I am going to take a crack at is to use one of the points in the feature itself. I'll probably just pick the middle point and use that as the label. This should get the label reasonably close, and then let users make minor adjustments to its location in Google Earth.