Though Bitcoin holdings in wallets are expressed in terms of hash values and donot publicly reveal the name of the owner, the transactions from one address to another are always public (part of the block chain). By systematically studying the movement of coins in and out of a wallet, it is possible to unravel the owner.
A study of this nature appears to suggest that US Government could be one of the biggest holders of the Bitcoin wealth arising out of seizures during criminal investigations.
Naavi
