Wildebeat wraps up its reports on hiking poles. From his script:

JULIANNE ABENDROTH-SMITH: Well what we saw in that study was as — at the lesser slope, the fifteen degree slope… some people used the poles very effectively, a lot of people didn’t seem to make use of the poles at all whether they had one or two in terms of going downhill. As the slope got steeper, then we saw a distinct difference in terms of both men and women tended to use the poles, did much better in terms of un-weighting, especially men, lessened the forces really well. Women didn’t un-weight so much, but seemed to use the poles as a balance factor. Then at the steepest slope, when we got them at twenty five degrees, then everybody used the poles much better in terms of being able to un-weight or being able to lessen those forces on their joints. And two poles was still better than one pole, but one pole is still better than no poles.

Steve also links to a fine site for finding pole tips: AdventureBuddies.net