I've just ordered this from Abacus Software:
"What makes for extreme landscapes?
Normally, Flight Simulator elevation info for the world is accurate to about 1220 meters.
World Extreme Landscapes boosts the resolution to 38.2 and 76.4 meters depending on the geographic area, thereby delivering up to 128 times the visual accuracy.
Below you'll see how much more detail is revealed when the elevation data points are closer together instead of 1220 meters apart. The resulting landscape is modeled even closer to reality and brings you an incredible visual flight.
With Microsoft Flight Simulator you can effortlessly travel to places that most of us only dream about. Flying the simulator is a certainly a great way to visit the world. From the dizzying heights of the Himalayas to the dense jungles of the Amazon and from the picturesque Alps to the remote, rugged headwaters of the Nile, there's an endless supply of adventures awaiting you.
By simply adding
World Extreme Landscapes you'll instantly transform these places into even more magnificent views. Based on Flight Simulator's adaptable elevated mesh terrain technology, we've boosted the detail up to 128-fold. We've replaced the default elevation data with super refined 76 meter (and 38 meter in some locations) information. The result is an incredible scenic accuracy bringing the Flight Simulator experience even closer to reality.
Step up to the heightened specatacles that World Extreme Landscapes brings to your flights.
Additionally, for your "flightseeing" pleasure you'll fly our pre-planned tours in a brand new Vans RV-6A. "
3 DVDs, 14 GB, $30.00 USD. I'll let you folks know if it was a good purchase. I'm looking forward to my birthday present this year.

John