I've just received a Rokkor 50mm f1.4 and it seems to be a very good lens.
I wont be able to get out and shoot with it until tomorrow but a few test shots indoors look good. Comparing it to my Rokkor 50mm f1.7 the f1.4 seems to be as sharp at f1.4 as the f1.7 at f1.7 and it seems to display less blooming on bright areas too. They both seem to have the same minimum focus distance.
The advantages of the f1.4 over the f1.7 seem to be...
As sharp at f1.4 as the f1.7 at f1.7.
Slightly less bloom on bright objects.
Offers more aperture settings at the wide end...
f1.4 offers f1.4, 2, intermediate (f2.2 or f2.5?) and f2.8.
f1.7 offers f1.7 and then f2.8.
All examples are via Photobucket and so will be mangled...
50mm f1.7 at f1.7, 100% crop of my alarm clock...
50mm f1.4 at f1.4, 100%...
Sharpness is about the same but the f1.4 seems to display less blooming and therefore looks a little sharper.
Artificial flower shot with 50mm f1.4 at f4, 100% crop and you can see the pattern in the fabric...
I think I'm going to like this lens even more than the f1.7.
It'd be great on a body with IS, a max shutter speed of 1/8000 and a base ISO of 100