Version:           2.4-snapshots (using KDE 4.4.6) 
OS:                Linux

It would be good to have a visual information of what you are doing when you move the color curves. Slangkamp told the actual interface was decided after a lot of discussions to approach the photoshop model, but in Gimp and in Photoshop you have sliders for each color in the same window - like the Krita hsv adjustement filter, actually -, and it is a much more easy and fastest way to tweak the color
in a fast workflow.

Reproducible: Always

Steps to Reproduce:
Select color adjustement curve, choose a color channel, move the curve.

Actual Results:  
Move the curve in all direction, wait for the preview, and try to understand what 
modification you are going to get ( I exagerate a little bit )

Expected Results:  
select the color curve adjustement tool, move the sliders between cyan and red, or magenta and green, or yellow and blue. It should work with cmyk colors too. Do it fast, accept or cancel you tweaks.