I have started to soak them. In the dry climate here it seems to help. I'm taking my queue for the anecdotal evidence given in The Grape Grower about increases callusing after hydration. I have been giving the cuttings a 12-24hr soak in warm water prior to rooting. I have seen no increases mold or mortality, and it seems like they do better. It looks to be especially beneficial when the cuttings have been stored or shipped prior to rooting.
Wills, thanks for brining it up. I was planning on asking as well, I'll be interested to hear what other members have to say.