You can run two together to provide no single point of failure. Today there are 150,887,000 people connected to the Internet. LinkProof's traffic management ensures the fastest content delivery for networks with multiple connections to the Internet. Each is with a different provider, and terminate into 2 cisco 2501s on our end. We have several IP blocks from each provider.
Outbound traffic is done with static default routes.
Inbound traffic is balanced by assigning the ip blocks internally to different machines until it balances. It does not run on the routers or servers. Router1 has an ip from a block of ISP1. Router2 has an ip from a block of ISP2. 2 to each provider.