The subnet of IPs the datacentre gave us was apparently on loan, so they assigned us a new block and gave us two weeks to swap them over, during which both will be active. They're on totally different networks and subsequently have different gateways. The machines are a mixture of Debian, Ubuntu, Windows 2003, Windows 2008 R2.
Is it best just to add the second gateway with a higher metric (numerically speaking)? Most of the documentation I've found for running multiple gateways has been under the assumption that both will be active indefinitely. Whereas I'm after more of a failover model.