Pixagogo adds a KML feed next to its RSS feed for labels, containing all the latest photos for that label, ready for viewing in Google Earth.
What you really need to do to get this to work properly is: Grab the URL of a particular label’s KML feed, go to Google Earth, add a network link, and then paste the URL into the source field. If you just click on the KML feed link in your browser, you will open a static file.
What Pixagogo (and several other sites) could do is offer up a ready-made KMZ network link file that links to the feed, rather than just the feed. This makes subscribing simpler and easier.