This is a possible use for a paper bitcoin wallet
key-pair (well, public address + private key in two formats). I'm a great fan of such rather than trusting myself to stay ahead of all bitcoin-related computer malware.
Maybe you intend to give a 14-year-old relative a bunch of money when he or she turns 21. If you send the money to a public bitcoin address and tell the person what the address is, but don't give them the private key, then they can see the money has been set aside but cannot access it until you give them the private key. Of course, you can withdraw the funds at any time, but the general idea here is that you don't want to jerk them around and as long as they don't do anything too outrageous until their gift matures then they will receive it as promised. So the 21st Birthday Key to the Door
can become the 21st Birthday Key to the Address in BlockChainVille
In addition, if the value skyrockets as many think it will, a relatively small number of bitcoins now might just result in that average BlockChainVille address becoming a very swanky address indeed.