Wow! What method did you use to create it? In particular, how did you get the stroke on the coastline? The colour choices are stunning and the coast fractalisation and land mass distribution is really believeable. What sort of scale were you aiming for?
The only thing is the mountains where you've got the plateau effect going (which suggests clippling on the heightmap), but it's a really minor quibble.
Did you do this in Gimp? I can't wait to see more.
You know, this is one, when you've got it finished, to definitely consider professionally printing.