Shape2KML works within ArcMap 9.x to convert points, lines, and polygons to KML for viewing and manipulation in Google Earth.
Seems like a very simple method to convert shapefiles to KML. Unfortunately there isn’t any source code to see how this was done and make improvements, but I’m sure any feedback to the author would be appreciated. I’m still on vacation and not near my license manager to check this out so anyone who’s tried it, post in the comments what you think.
Thanks to Ray Carnes for pointing this out to me. Good eye!
**Update - Mike points out in my comments that a VBA script that converts a feature layer into a KML file. It only exports linear features right now (input can be point, poly, line), but at least this one has the souce code. :) **