For everyone that said it helps in terms of providing more stability because of the weight I completely agree. I find the size of both the D7000 and D800 just right with the grip on and that extra weight helps in terms of inertial stability. At least for me it is just so much easier holding something heavier more steady. And it also depends on the kinds of lenses you use. The balance with larger lenses is almost essential otherwise the lens becomes too front-heavy.
Imagine how ungainly this combination of D7000 with 85 mm 1.4G is without the grip...
Or with something like this on the camera, it becomes even more important to have that counter-balance (yes, to me the 300 2.8 isn't even really that big

).
If I'm not using the grip, I feel like I'm just taking snapshots, but with the grip somehow my attitude changes and it is all about more serious photography.

They are fun to use...