The only issue I have yet to resolve with respect to doing line art on Linux is how to temporarily disable the blended font display (on Windows it's called ClearType) when using the text feature to label stuff. If any Linux users here know what to do about that, I'd love to know.
I use GIMP for the text. I find KolourPaint great for drawing, but I still haven't figured out how to temporarily turn off the anti-aliasing. GIMP is very complicated to use for drawing but turning off the anti-aliasing is easy, so it is great for text.