It is not yet decentralised.
The planned "decentralisation" involves bitcoin blockchain transactions that need many signatures, so you can do things like "it takes any 30 of these 50 servers to sign in order for these bitcoins to be moved".
At that point many Open Transactions servers can all as a group secure bitcoins into the bitcoin blockchain in such a way that a majority of them have to agree where those coins are to go in order for them to go anywhere.
That "federation of Open Transactions servers" stuff is not yet in place.
I am currently testing Open Transactions, see https://bitcointalk.org/index.php?topic=53329.0
-MarkM- ("knotwork"; Digitalis Data Services.)