Add: Kol.klink is right on the point of comfort and stiffness. There is still a very large difference in terms of cost between a quality steel fork and a carbon one. For a work bike as a messenger, carbon fork doesn't make sense.

1" Threadless is a bad idea all around - especially going carbon. Instead of rewriting Sheldons post i'll link to it instead:

http://www.bikeforums.net/showpost.p...75&postcount=3