It is quite time consuming, yeah... but I enjoy doing it
One of the reasons I don't use Gimp much (I have it installed) is because I don't like the layout. It's annoying for some reason.
I've also tried my hand at photoshop, but let's face it. It's quite expensive AND difficult to learn.
If I ever finish my book, which (hopefully) I will... Then I'll most likely draw a hand-made map for the books instead.