Nice! I’d love a Cintiq. Using a Intuos3 A4.
If I’m not using real world data, what I do roughly is this:
Make a selection with height selector so that you select for land falling away to zero at the coastline. This means that you get smoother coastline areas which kinda mimicks nature- more sediment deposited there.
Fill that with Noise from a Advanced Perlin. Use a Clamp device immediately after the perlin to set the height variations of it. This will create your general undulations (not hills as such).
Now you want to create a mask which will go into the mask input on the advanced perlin. This will tell WM where to put undulations. For the mask input I’d create a mask for my rivers and anywhere else I didn’t want noise. You want to use an inverter device so that WM puts noise NOT on the rivers 
I would also the blur just a little bit so that you get less noise closer to the rivers. You can add two masks together with a Combiner in Add mode. So you can get a complicated mask slection of various features going into the adv perlin. Multiply and subtract modes can also be useful.
You can draw your masks in a paint prog or you can use a layout device. Right click on the device and set hints to Mask. And click the checkbox on the left in Layout mode to Display as Mask. You can use the lower of the two outputs on the device (Shape Mask) to output a mask as extents (ie a on/off mask of black and white), or I think you can use the upper one as a mask which has internal variation- ie it keeps all of the grey variation.
So with layout you can draw your mask areas directly within WM layout. To give the selections a more natural feel use “Use Breakup” on the left in Layout mode.
I’d draw mountain ranges as a network of ridges using multiple Spline Shapes in Layout. You want the mts merge together but I think the default srtting in Layout allows that anyway. How they get added to your underlying terrain will be a combination of the Combiner device setting you use and also the Shape Properties (Right click the Shape you drew in Layout and Edit Shape Properties). The Default value height has the biggest impact.
Then you can combine those with Advanced perlin (clamped) to add natural variation, although the fractal breakup might do the trick. Fractal breakup though tends to have some unpredictable horizontal displacements.
The Chooser device is useful for replacing one area of terrain with another.
Another more advanced trick is this: Create your basic land shape, including your general noise. Mask for your coastline and rivers, etc. Create simple layouts for hills and mt placement. Erode everything heavily with chanelling erosion (channeling, channel depth and maybe post channel to max). Drive it as hard as you can but so that you are happy with your coastline. (always use accurate setting in the layout view for checking). Output a mask from Flow output on the erosion. Save out the flow map using a bitmap output device temporarily hooked up to your flow output on the erosion device… Basically you want as detailed a flow map as you can get- lots of channels. You might even try an equaliser device on the flow map to get more detail contrasting out.
Then import the flowmap and use it to mask the advanced perlin or any other device you are using to create land. Again you need to invert the mask. You should be able to get more natural land forms that way. All of those flow lines will be masked out and you’ll see better terrain. Again, use a blur on the mask to get more natural effects.
If you really wanted to push the boat out you could use real mts from the SRTM free data on the net. But you’d need an app to open the terrain and export it in a format WM can use. //edit: I think you can download as a geotiff and open it as a tiff in WM.
A recent test I did for adding angled strata: http://www.skindustry.net/medem/files/Phase2/Terrain_1.0/NASARun/2011/WM_tmds/MtMindolluin_strata5b.png
monks
