You don't need to wait to use your Bitcoin addresses. It's only that before the synching ends, or until it reaches the blocks where the transactions were confirmed you won't see them in your wallet and be able to spend them. But you can se them in a block explorer site.

For instance, the address where the kind people here sent you those little bitcoin gifts, you can see it here: http://blockchain.info/address/1CeoBMn9Qn7wygecmBybQ5WCRLDxrcoQnq
See the money already there?