Even if the use of these meta elements has been niche, one isn't the loser when a site doesn't provide them - the same as with alternate stylesheets, feeds, universal edit button and similar stuff. Usable for testing. Existence of such a feature can nudge developers to include corresponding meta data in their pages.
I discovered Geo when I was looking for something to test my new geocoding of my WordPress blog http://bkkphotographer.wordpress.com .
Geo works well. I am looking for other geocoded web pages. My only enhancement suggestions are a) make the annunciator that a page is geocoded a bit more prominent and b) put a pin on the Google map showing the exact location (if possible).