I ran across this thread a couple of days ago and started playing around with Gmap4 yesterday. I wanted to create my own printable map of the AT centerline with all the shelters shown on the map. Knowing absolutely nothing about KML, KMZ, GPX or any other such geographic data file, I encountered some difficulties but once I figured it out it was super easy! (A quick email to the OP and his superfast response was a huge help)
The OP has created a great tool for hikers or anyone else that enjoys the outdoors and knowing where they are out there.
I created this map and I want to share it with you guys here on whiteblaze. There are probably others out there like it, but hopefully it will be of some use.
At Centerline with Shelters
It works really cool zoomed way in the the MyTopo feature turned on. There's a lot of information there.
By the way, the whole trail may not show up when you first load the page. Just zoom in a click or two and it should be fine. (still not sure why that's happening)