This lens is just so good compared to the best that the "L" zooms can offer. I have "L" zooms but this is better. The build quality isn't the same but zooming isn't alchemy. You compromise to zoom. I used to shoot 35mm mostly wtih a Nikon 105/2.8. This 50/1.4 is great for available light and moderately long on a 1.6 crop digital camera. It is a great available light lens. The 85mm 1.8 is also great, and matches what my 35mm eyes are used to, but the 1.4 speed lets you take available light shots without silly ISO speeds at great resolution. As you go longer that speed translates into shallow DOF and perfect focus is necessary. I have a Canon 20D. I can focus manually exactly where I want, but even the 20D can't automatically figure out where subject sharpness matters and drop off doesn't bother the eye.
The 50/1.4 doesn't have the same build quality as the "L" series, but it is an insane bargain and the budding photographer would do well to add it to their kit and learn to use it before zooming. Zooms are a guilty pleasure and a crutch. YES - I HAVE three "L" zooms, but I like available light shots and the best stuff I have gotten is with the 50/1.4 and the 80/1.8 both add up to less than a 24-70/2.8 (which I have)
The ability to shoot at 1.4 counts for a LOT.