How about when they are granted super-user access and can see everyone's hole cards? Can't help but remember the Absolute Poker and Full Tilt cheating scandals. Correlating moves was eventually how the culprits were caught. But only well after the fact.
This is just a temporary solution that will end up buying his site time if the US DOJ decides to shut it down. While I personally think the security risks of Bitcoin outweigh the conveniences, considering that online poker probably isn't going to be regulated anytime soon in the States - http://onlinecasino.net/blog/united-states-online-gambling-bills-update/ I can't blame him for trying. As long as his poker site doesn't get as big as Poker Stars, it probably won't become a target for the U.S. government. Bovada will be the first if the DOJ decides to still go after operators....although I think they are finished following the DOJ's new stance on the Wire Act.