The terrain in the first example looks like it was done in PS (the Distort - Glass filter on the river gives it away but I don't know if GIMP has something similar or not) and the buildings look like City Designer 3. The thing is, making this map probably took at least a few days. You could probably bang this out in one day with enough practice, though. The maps on the website look like PS with lots of patterns. The main thing is that speed comes from practice...but I'd expect to chew at least a whole day making any map. The fastest guy I know, Gamerprinter (member here) uses Xara something or other and the second fastest guy I know, Torstan (member here) hand-draws and hand-paints everything in PS with a tablet. I could probably do a lot of what I do with actions that would speed things up but I like to really nitpick everything I do.