Review copies are something less than gifts. Each party has some expectation. Reviewers agree to consider the book for a published write up of some kind, and publishers expect their overall return (in increased public awareness, specific sales generated, etc.) from sending out x number of review copies to significantly exceed their costs. Publishers hope to get more out of the "deal" or they wouldn't do it. For many reviewers, the book itself is the only renumeration for a significant expenditure of time and effort, and I think it more than reasonable that they receive their copies sans markings. Maybe the Civil War corner of the publishing world is simply a more generous place than the rest, as I've gratefully found hardback stamping and paperback ARCs to be a distinct rarity. Over 90% of the review copies I've received from publishers -- big press, small press, university press -- over the past 5+ years are first editions, and I could count on one hand with a couple fingers left over those that were stamped. I personally appreciate this gesture as I am a fervent collector, too, and condition is a big part of the game.
What inspired this discussion was marketing director Sarah Keeney's post on her blog promoting a publisher's perspective on ink stamping review copies. These markings can be downright ugly or relatively unobtrusive (e.g. a prominent university press stamps them with a mascot paw), but regardless they permanently mar the book's appearance and collectibility. I understand the thinking behind the deed, and the issue is rather immaterial with ARCs, but it always annoys me as a reviewer, collector, and general bibliophile to see a stamp placed inside an otherwise pristine first edition of a valuable book. Thankfully, the vast majority of publishers I've dealt with eschew the practice, and I would urge Sarah and her original correspondent to reconsider their plans.