From the FAQ [1]:

We are also offering the ability to have an entire /64 or /56 subnet routed to one of your IPv6 addresses – even one of the Pool addresses, which means you can fail over the entire subnet.

[1]: http://www.linode.com/IPv6/

Each Linode, by default, has one IPv6 address. Via ticket, you can request a /116 pool, and any of your Linodes in the datacenter can bring up any addresses from that pool. You can also request a /64 or /56, which gets routed to one of your /128 or /116 addresses.