There are a number of folks here who use it and others as well. I know there are a bunch of tutorials on the rp-tools website that show how to use their paint tools to create a map but I think you can also create it in just about any program and open it into maptools to add all their clicky stuff. I'm no expert however in using it. I have created a few battlemaps for it but so far not a world map. I think you can do it, it just has to do with scale. From what little I think I understand you could make a worldmap and then have individual battlemaps that you would use as needed. I don't think you create one huge world that will work as a battlemap....too much memory required.
There are other tools that might do that better. Redrobes' for example might work that way.
I guess the question that comes to my mind is "What is your goal with this map?"