A 50mm is perfect on FX. The 1.8G is widely regarded as one of the sharpest, yet cheapest new lenses you can get. It's too cheap not to have! I bought one recently, but like others have said, the 24-70 2.8 is just so great I don't see much need to use the 50mm. Where I do like to use it is for portraits of the kids, indoor, ambient lighting. The 1.8 aperture is great for catching as much light as you need, and blurring out distracting backdrops. You have to be critical with your focusing though.
It's a sweet lens. And of course, it weighs hardly anything, so it's also perfect to just stick on your camera, leave the rest at home, and go shoot some street.