Multi-host nova-network HA is not supported (i.e., running nova-network on each compute node for HA purposes).
CloudPipe VPNs do not work when using Quantum Manager. Nova is developing an alternative to CloudPipe for Essex that should be compatible with Quantum Manager.
Horizon cannot be used to create/delete networks, or view networks and ports. There was an initial version of Quantum + Horizon integration, but this was not compatible with the Quantum Manager in Essex, and was removed as a result. Likewise, Horizon does not support specifying multiple vNIC on a virtual server, or indicating what networks those vNICs should be attached to.
If networks where created using nova-manage, you may use Horizon to create/destroy virtual servers, which will then be attached to all "global" and project-specific networks, as described above.
In Folsom Horizon will fully support Quantum.
