I had a rack like the Nashbar front rack, and mounted a Wald basket to it. I carried a gallon of water in the basket, and the fork crown brace BROKE. I mean the metal separated.

I now use a Soma Mini Front rack. If you have rack/fender eyelets on your fork, it's a much sturdier setup.

http://store.somafab.com/somialfrra.html

By mounting to the eyelets AND the fork crown, it spreads out the forces. Soma rates it to 20 pounds of cargo, which is a lot more than the racks which mount to canti posts.