I heard about this recently on the podcast, Sticks and String. He was using it for picking up stitches around armholes and neckholes and was using the Addi Turbo Cro-Hook
(it's the 5th item down on the left column). Based on the link, it looks like this one only comes in one size though and I don't think it's really meant for using for an entire project. Sounds like it's meant just for the ease of picking up stitches, and then you knit off of it onto your regular needle.
Boye also makes what's called a cro-hook, but it's a double ended crochet hook, with hooks on both ends.