@DH, after sending a transaction using old coins existed and generated prior to the block 460,000 couldn't either parties(nodes) be programmed some how to cross reference the both chains to see if a transaction is being double-spent? and how can someone send your coins from other chain without your permission if they don't have the private key?
Also miners could as well ignore all transactions and mine empty blocks for as long as it takes to sort things out correct?