I was never really able to take full advantage of all that my tablet had to offer with the Gimp. My biggest issue was the pressure sensitivity was simply just going to waste. On a whim, I downloaded WinGIMP and plugged my Wacom into my windows box to see what it looked like, and while support for the pressure sensitivity was there, it was really buggy.
Finally, I broke down and downloaded the 300+ meg demo of Photoshop from Adobe's website. What a difference it made. True, my art still sucks, but I can now draw very natural looking sketchy lines with a variety of brush effects. For sketching, having the size of the brush shape directly linked to pressure makes for a beautiful looking stroke.
Someday, I'll have to break down and buy a version of Photoshop for my own personal use. I imagine that I'll end up using Elements or some other scaled down version. In the meantime, I'm putting Photoshop on my wish list in case there are any among you feeling particularly philanthropic.