Did I write all that?? :shock: Was that the short answer? Well at least I know your are still reading this, which means I wasn’t boring enough… So give me this second chance! 
Right! Now for the techies…
I was under the impression the topic of islands had been mentioned earlier, but I can’t seem to find it… Anyway, the problem of placing a mountain in the middle of an ocean, is the same as placing a beach near the water, or placing a volcano 2 miles north of the second pool to the right… The way you do this in WM is to have a mask for where you want to place volcanos, or beaches… Notice, you place “volcanos”, and don’t place “the volcano”. So, in theory, for the island you want to mix two terrains (flat_water and mountain) together.
[I don’t know what is the best way to explain this, so I’ll try to transmit my way of decomposing tasks, and try to use it to pass-down the logic]
The chooser device:
Think of your problem in the same way and complexity as the devices you use. The chooser device, is the most common device for choosing between things… It has 2 inputs for terrains to be mixed (or choosed between) so it is useless to think in more than two things to choose from a t a time. So if our island is composed of water + mountain + beach + cliffs + volcano, we should only choose between water and “stuff” (where “stuff” is the choosing between “stuff2” and “stuff3” (where “stuff2” is … (((…)))) and so on…
To make the choice you only need a mask (terrain similar to others that is interpreted as weighting value). Imagine each pixel of the mask to be a value between 0% and 100%, and the final result of choosing on that pixel position will be x% of terrain A + (100%-x%) of terrain B, where x is the value of that pixel.
The other devices:
So this sounds theoretically good! The problem usually is more to have the volcano in the right place, so you can shoose it there… This is, IMHO, the problem that the WM-er must solve.
(To understand the problem imagine overlapping and island and a terrain full of volcanos. Imagine now that there is no volcano over the island. the only solution whithout translating anything is to push randomize button. it’s probably more boring to push randomize buttons, than to read this text 
)
So back to our problem, we need to model our modelling according to how WM works. We have to think of ways to create things from what has been built already, to serve as clues for WM to do what we want.
Very well the island!.. I’ve been writing so far and have not made any island… Play with a perlim noise until you get some moderatelly spiky terrain. use a clip device to clip the lower 50% of terrain (in “clip” mode)… Ok, instand unrealistic island: “just add water!”
Play a bit more to have larger islands so we can have room to place beaches and stuff…
Now if we followed what I said about the chooser device, we would like to have a terrain looking like a beach (dunes macro) and choose between normal-island and dunes! Now we can’t just choose between them like this, because 1 both terrains are at different hights… We will also need 2 to create a mask to say where the beach is… For problem #1 we can use the chooser in “add” mode, for problem #2 we need to think of a way to use what has been constructed already as a starting base for WM to create the mask. Very well let’s think on what we have: a terrain mostly flat that suddenly has mountain, and we want that mountain to have a beach at its base. To do this you can use a height-selector to select the height range to replace by a beach. While you select the values for the height-selector, keep checking the preview window to know the space the beach will occupy. Choose something between 0.00verylittle to 0.0something
By this time you should have understanded that you can create an island with a few dunes and an ugly mountain in the middle. For this you should have already spent a lot of minutes adjusting the variouses devices’ and macros’ parameters…
Now you could also have made use of transform devices to change the result from the select-height device in order to have more “room for maneuver” when selecting…
Also, if instead of a clip device, you would have used another height-selector, you would feel the need to keep both this and the other height-selector for the beach mask set up to the same height value… For this you would probably whant to use the scalar devices.
So as you can see the device net can spread like weeds in a jumgle, so thanks, Stephen, for giving us Macros. That is what I use them for… When I get to a point where something is conceptually solid and “nameable”, I turn it into a macro.
Conclusion:
So the first long post was to warn that this hadn’t one solution.
This second long post is to say that, there is no one device that can do what we want (notice my first post suggested a chooser for the island and sea, and I ended up suggesting a quicker clip device); and that independently from the terrain we are building it is very usefull to think the same way WM “thinks”, so that things are created with the logic we intend them to be. (beaches where we want)
I also left this island issue open, because I think it is too broad and too adequate for each of us to explore on our own. It deserves the parental dedication we can give it so that different solutions can florish…
[Are you still reading this?? I must think that I am a poet or something… :P]
Good WM-ing to all of you
Then you also need to know how to compose them in the right places… And for all this you need experience, practice, and a decent manual (this last topic is being taken care of).