Is there a service that automatically "sweeps" funds to another address whenever they are sent? There's the sweepprivkey proposal from 2011 which was not accepted, that would have allowed one to instruct her bitcoind client to listen to transactions and sweep funds whenever they are transferred from one address to another.  

There is also this question, "Is there a way to automatically send bitcoins from one wallet to another?", but it does not specifically ask about a service that would do that.

I was wondering whether someone developed, or is considering the development, of such a service. 
There would be security implications, as the service would have to know the private key of the address to sweep - is there any secure way to implement this otherwise?
You could make one using bitcoinj which listens for txns, then triggers a spend.
Perhaps you would use rpc to control bitcoind to make the spend, and only use bitcoinj for the listening side ?
That should (I haven't done it but hope to soon) not require any private keys to listen to the wallet.
See this: Listening to all transactions of the Bitcoin network 

bitcoind appears to be pull oriented, while bitcoinj can be set up to be push related, sort of.