It depends. There's a small issue with the reference client that is also causing chains of double spent transactions in merchant wallets: http://www.reddit.com/

It depends. There's a small issue with the reference client that is also causing chains of double spent transactions in merchant wallets: http://www.reddit.com/r/Bitcoin/comments/1xm49o/due_to_active_malleable_transaction_relayers_it/ http://www.reddit.com/r/Bitcoin/comments/1xm49o/due_to_activ... I would be more inclined to believe that the majority of sites use the reference client and this is why issues are appearing.