First try at Fast Artistic Maps In Gimp
Here is my first attempt at using the very easy to follow tute as mentioned. Not perfect, by a long shot, I know, but I plan on working with the style.
I am into this style also, could you tell me how did you do the houses so they don't overlap? I followed the tut but I can't seem to find any reference to it, my houses are see-through .Your map is good for a start, but try making forests a bit more irregular and try not to "end" a mountain chain with high mountains, surround it with smaller hills so it appears more natural.
Oh and try playing around with textures, layers and such, you can make nice variations of the style explained in the tutorial. Good luck!