I'm getting myself familiar with vector-based drawing in Inkscape.
I'm not that much of a graphics person, but I can draw one mean symmetrical batman logo - gotta love the cloning.
I've used GIMP briefly, and I need to start figuring that out. I'm also interested in writing small scripts in python (once I learn that...) and see what all I can make from that.
I've used Paint.NET a little too back when I mainly used Windows. I plan on seeing how MonoPaint, a port of Paint.NET to the Mono platform (meaning it'll be availabe on Linux), goes and if it'll can be worth more than GIMP.
KColourPaint is kinda fun too - a simple editor modeled after MSPaint (with most of the features the same).
About two to four years ago I used Adobe Photoshop (I think I had version 6 at the time). I dabbled in it some, looked at some tutorials 'n stuff.