Not as sharp as the 50, two-thirds of a stop faster, quieter focusing, £200 more expensive. I like mine, but I'd rather have my 50 f/1.8 and if I needed the extra two-thirds of a stop the 50 f/1.4.
but then again i went for the 30mm as once you've taken into account the Field of View Crop, you end up with a 45mm equivalent on the D80. The 50mm gives you a 75mm equivalent. Saying that, im still going to get a 50mm, either the f/1.8 or hopefully the f/1.4
And depending where you buy it from only £160 more expensive

It really depends what you want. I wanted to get a "near as damit 50mm" for the D80.