Sounds like Microsoft Live.Local and Google Maps/Earth are heading for an out-and-out battle for maps.

I have created my "google map" yesterday.
Have fun : http://www.maplib.net/map.php?id=37

"Colors, opacity, and even descriptions are not preserved in the Google Maps display"

I've had problems with that. Google Maps seems to get confused by the StyleMap element generated by Google Earth causing it to use the wrong colors. If you hand-edit the KML to replace references to StyleMap elements with references to Style elements, it works a lot better. At least for me.

Here's an example from Google Earth:

http://www.windypundit.com/archives/2006/images/DesPlainesTIF-GEcolored.jpg

Here's the busted version on Google Maps (at least until they fix it):

http://maps.google.com/maps?f=q&hl=en&q=http://www.windypundit.com/gis/2006/DesPlainesTIF-GEcolored01.kml&ie=UTF8&z=15&om=1

Here's the edited version that works:

http://maps.google.com/maps?f=q&hl=en&q=http://www.windypundit.com/gis/2006/DesPlainesTIF-Zones-05.kml&ie=UTF8&z=15&om=1

So, I guess the workflow is to use Google Earth to capture the geometry and then hand-build or script the KML to get the appearance right.

[Prediction] Google will probably create a web-based version for creating KML files and they will integrate community driven functions/content into Google maps.

Mark, thanks for the info – good to know.

About the MapLib.net link. Via http://digitalurban.blogspot.com/2006/12/gigapixel-panoramas-viewed-in-google.html , I bumped into this amazing gigapixel image of Boston (http://www.xrez.com/boston_giga.html) that is presented as a Google Maps image (hooks directly in on the Google Maps API, not on MapLib). For those interested, there is more: http://www.xrez.com/gallery/xRez_gallery.html