I tried out this curve originally and found that it indeed boosts low tones, however, the midtones from some of my shots (specifically, the brown spots on geese)lacked contrast. You really have to understand what the different concavities along a tone curve correllate to when you create custom tone curves. I've attached a comparison of the different curves.
The black dots indicate the waypoints on my curve while the red dots indicate the waypoints on the JLMcurve. One thing I've noticed about the JLMcurve that I do like and want to try and change on my own curve is how the midtones are darker. This has the effect of making skies look deeper. For now, I use a circular polarizer to create this effect. I haven't been able to find a way to create the same effect while maintaining contrast and brightening low-mid tones. http://genji.image.pbase.com/u17/atmabini/upload/7888628.D100TONES.JPG
In summary, whenever a portion of the tone curve is concaved downwards, there will be a loss of contrast because tones will be clumped around that portion, whereas, wherever there is a straight line or concavity upwards, there will be an increase in contrast. One other thing to note with Nikon's implementation of custom tone curves is that you cannot alter separate RGB channels, thus, when you bend the curve, you risk altering the curve for some colors more than others. What I've noticed, subjectively, is that red seems to react to the bending less than the greens or blues. In order to avoid these color shifts, as well as maintain contrast in the low-mid tones, I kept that portion of the curve straight, but increased its slope. In order to avoid blown highlights, however, I started to introduce a concavity downwards "tail" at the end of the curve. This has the effect of making highlights softer and retaining slightly more information in the highlights. In any case, try out the curve yourself and see if you are satisfied.