I'm not aware of any payout problems.  I believe there was one guy complaining that one of his withdrawals was flagged for manual processing, but that it was resolved quickly.  I can't recall now whether I saw that in the Nitrogen blogs or in a forum here.

It seems like not all users have similar expectations from BTC books; some want complete bilateral anonymity, including freedom from any AML practices at all.  Personally, I would be willing to put up with AML practices that parallel current practices at sportsbooks denominated in fiat currency in exchange for knowing that the sportsbook is a real company staffed by multiple humans in a known location.  

Nitrogen seems to be closer to a fiat sportsbook in terms of its own anonymity, so I expected that they might manually review very large withdrawals.  However, my withdrawals from Nitrogen have always been immediate.  When I withdraw to a Blockchain wallet, the coins appear in my account within a few seconds.  This is clearly too fast for any manual processing or approval at all.  If anyone has been experiencing non-instant withdrawals, that would presumably indicate either a server issue somewhere or some sort of flagging of their account in particular.  I've made ~10 withdrawals in amounts from 0.05 to >4 BTC and all were equally fast.  Since they also credit deposits instantly (even with 0 confirmations), it would be practical to use Nitrogen as a sportsbook while using, e.g., Blockchain for your wallet.