Ok great, so I take it my supposition is correct and the account names can not be found (without actual security breach) from any public or private record other than what me and my bitcoind have given out?
I'd think about it this way:
You have rooms in a hotel. Make sure the key-card works for the user's room, and that room only during their stay. The key-cards are interchangeable and easy to duplicate, but relatively secure as they're assigned to a specific room.
Could someone in theory "discover" their neighbors key-card code and use it to access their room? Probably yes. Though it would take a brute force guess or some other form of error (ie. they steal that persons code, and duplicate it while it's active: this would be analogous to someone breaking your web-app or interface or whatever and stealing the associated account information).
That's where the house safe comes in, last resort - the valuables (coins) are sealed in cold storage, and all they get is account numbers / public-addresses / balances (synchronized with the bitcoind client that links you into the bitcoin network) but once inside that info is worthless for much more than information sake without the private keys which are stored offline -
I think there is certainly a market for this type of product when someone builds it (I know proprietary shops have built it and maintained it...but they're not giving it away...)
