SOLUTION: Wrap the send packet with the receiving BitCoin address, so only the receiving BitCoin client can un-encrypt the packet and transmit the packet back out to the network. Thus, the sender can be assured he is sending it to a real client.
If you don't require the receiver to be online, then this would add a level of complexity to the Bitcoin system. The transaction needs to persist somehow until the receiver gets online.
(EDIT: You probably want to define a TTL in any case. The coins need to be blocked for the duration of TTL, otherwise the wrapped packet will be invalid.)
If you have your wallet backed up, you can just restore your backup wallet.dat. Since the last transaction is not verified, your bitcoins will not be spent.
If you enter a broken address, there is a good chance that the transaction will not happen in the first place (because of the checksum). I think he's talking about cases where a transaction goes out, in which case it will surely get confirmed.