Someone in the Rifle forum mentioned in passing that it would damage the stock, because of the reason stated above, that the recoil is all absorbed by the stock. He said some custom stock manufacturers advise against the use of the Lead Sled for that reason.
I just bought one at Cabela's, but am thinking of exchanging it for a more stock-friendly rest, unless you guys think that, as one of you already said, it won't hurt anything with limited use.