I use inkscape for overland maps. I use Watabou Medieval City generator for city maps. I use Dungeon Alchemist for dungeon/indoor battlemaps.
I think that main problem is lack of support for the former. Some people really like to do that, but rolling your own is hard. There are some third party supplement that might fit.
I use inkscape for overland maps. I use Watabou Medieval City generator for city maps. I use Dungeon Alchemist for dungeon/indoor battlemaps.