According to reports that have been surfacing from Motorola Droid owners that have received the update to Android 2.1, Google Earth has not been accessible via Android Marketplace.
According to DROID owners, while some can access the application on the marketplace at this time, many cannot after receiving the 2.1 update. This is an interesting occurrence, as previous downloaders of the Google Earth app (Either being a device that was update sooner or was manually updated) can no longer see it on the marketplace, but can still run it locally on their device.
Google has commented that the problem is only affecting some users and they are working quickly to resolve the situation.