A lot of local guys raced those Dura Ace tubeless rims this winter, and more than a few of them ended up denting the rim running low tire pressure. It makes perfect sense, since the rim profile is the same as a standard clincher rim. Sure, it does away with the problem of pinch-flatting on clincher rims, but tubeless doesn't address the few extra mm of rim that are still going to come into contact with that log or branch (or curb) if you're running low tire pressure.

Oddly, I haven't heard many complaints about this from mountain bikers, but then I don't really ride much mountain stuff myself and I don't know what kind of tire pressure they use.