My problem, in addition to those already stated, is that

(a) I think that ICM, the registry operator, is intentionally rigging this to rip off the adult industry;

(b) ICM is being completely disingenuous by stating on the one hand that it's voluntary, and a few paragraphs later, stating that "parents want a way of protecting their children." Those statements are fundamentally at odds with one another

(c) ICANN stood by and watched the .info and .eu registries get totally corrupted during landrush and sunrise periods. There's no reason to believe they'll do any better with .xxx.

(d) As Steve points out, zoning has to be consistent to work. Unless (unlikely) there is complete agreement among ALL countries, with equal enforcement, all .xxx will do is force webmasters offshore.