1: Create two (small) images describing how you want the map to look, the first one contains
Red: Average height
Green: Unused but will probably describe how hills look later
Blue: Bumpiness, how much randomness will be added to the average height
Second one
Red: Metal density
Green: Forest density
Blue: Geothermal density
2: Run mapgen with these files and a random seed as arguments, it will output a heightmap, featuremap, metalmap
3: Input heightmap into terragen and generate texture
4: Run mapgen again but this time also add the texture map as argument, this will do the same as step 2 except it will also modify the texture map with metal spots
5: Take these files and input them into mapconv
6: Create a smd by hand
In all it should be possible to create a new map with 15-30 minutes of work and 6h of waiting on terragen.
For Island Divide i used

and

as seed images. They might look a bit complicated but looking at one channel at a time they becomes quite easy to understand.
The resulting map looks like

http://taspring.clan-sy.com/temp/id001.jpg
http://taspring.clan-sy.com/temp/id004.jpg
It can be downloaded from
http://fileuniverse.com/?p=showitem&ID=3155
Im not quite happy with the mapgen yet (only support 16x16, hills doesnt look that good etc) so i wont release it yet. When I have fixed it a bit better I will probably release a 14x14 version of this map as I think it could lead to more intense games.