Inkscape might be a better choice. The tools are dramatically better for incrementally improving a basic idea. The GIMP rules for bitmaps, but vectors are a better tool for the job for a lot of stuff...like icons and such. There's a lot of good SVG artwork out the to look at for inspiration, and even borrowing within the bounds of the license. The Tango icon set is a great source.

I'll also mention that we've only recently gotten serious about design and graphics, and we've been profitable (by some definition) for a couple of years.