Dallas Data Center / Rackspace

Linode is in one of the SoftLayer data centers acquired from The Planet, so no, they're not in the same buildings. Nonetheless, they are in the same city, and Rackspace and SoftLayer peer, so latency is still gonna be roughly zero.

Edit: I did another traceroute and they don't seem to peer over IPv6. But that just means one additional hop via an HE router that's probably in the same Equinix facility anyway. (I don't know if Rackspace's API servers support IPv6 yet.)

Thanks for the info. Sounds like I'm on a decent path.