In Gimp and other editing programs, there is a "levels" tool with 3 sliders: dark, light, and midtones. I find that a lot easier to use than the curve. I'm surprised that DPP doesn't have that same thing. In the RAW section of the Tool Palette, there's a sort of levels tool (with a histogram) but no midtones slider.
I'd be curious to know how folks use DPP to adjust their levels.