Jürgen Hubert
First Post
I've recently started a masters in landscape architecture, so computer-illustrated geography is a Big Deal. Our core four are Photoshop/GIMP, Illustrator/Inkscape, AutoCAD, and Sketchup. I think Photoshop has an ease of use that GIMP lacks, and documentation is a hundred times better, but much of the photoshop documentation can also be applied to GIMP, and GIMP's pricetag (free!) is hard to beat.
I had some issues with Inkscape crashing, but Illustrator rocks. Again, though, for the price (Free!) Inkscape is pretty awesome.
I use GIMP and Inkscape in combination with a graphics tablet - which makes drawing coastlines and other irregular shapes a lot easier.