The Google Blog announced a small update to Google Earth over the weekend. Google Earth now has new layers that integrate Wikipedia articles as well as photos from Panoramio.com.
There's no need to update Google Earth, the new layers are automatically visible under the Layers menu. That said, if you haven't already, check out the beta 4 version of Google Earth.
To access the new content when you're using Google Earth just look for the Wikipedia globe icon or Panoramio “star” icon and click them to see the associated content. For Wikipedia entries you'll get the summary and a link to open the full entry in your default web browser. The Panoramio entries show the photograph and offer links to add comments or upload your own photos via the Panoramio site.

In addition to the Wikipedia and Panorama data, Google Earth now includes information from the Google Earth community. Represented in Google Earth by a yellow “i” icon, the content comes from user posts and uploaded photographs.
I've always been a huge fan of Google Earth and with the new content it just keeps getting better.
If you like the idea of user generated content on your maps you should also have a look at Wikimapia.org, which isn't affiliated with Google Earth in any way, but it does have some nice content.