The Map overlays for Google Earth site (link fixed – sorry about that) lets you select a source of imagery (Google, Yahoo, Ask.com, Windows Live, OpenStreetMap), and create a KML file that overlays that imagery onto the terrain in Google Earth, with definable transparency. Note: leave the lat/long offset values at 0; these values let you offset the imagery to correct for minor errors in position, not set the initial view position. You can also download a KML file with links to all the imagery, and select the source by checking the appropriate box in the Google Earth pane. Here’s Google Maps’ terrain view in Google Earth:

Warning: requires large and ever-increasing amounts of system memory (I wouldn’t try it with less than 2GB), will stress your CPU heavily, and loading in full-resolution imagery at high zoom levels can take a long time.
The maker of this tool also has a free software program called GMaps for Java J2ME-enabled mobile phones that displays imagery from Yahoo! Maps, Windows Live Local (MSN Virtual Earth), Ask.com, Open Street Map and other sources, and interfaces to internal/external GPS receivers.
Related posts:
- Overlay OpenStreetMap Data Transparently On Google/Yahoo Maps
- Positional Accuracy In Google Maps "My Maps" Vs. Google Earth
- Importing Google Earth Imagery Into A GIS
- Easy Display Of Thematic Data In Google Maps And Google Earth
- A PC GPS Application That Lets You Use Garmin Vector Maps For Live Navigation (OSM, Google And Bing Maps, Too)

You describe it, but don’t link to the actual KML generator or even say what it’s name is.
I think this is the website described in the article.
http://www.mgmaps.com/kml/
Matt, check this :o)
http://www.mgmaps.com/kml/
I’m pretty sure that app or the use of kml’s created from it it violates a lot of terms of use/service.