Please provide support of container monitoring (not just docker, but some general solution) out of the box. IMHO containers can be handled like VM:

• discovery of containers
• CPU metrics: CPU user, CPU system
• MEM metrics: ...
• NET metrics: ...
• IOP metrics: ....

Some metrics are available only if kernel is configured properly, otherwise metric can be unsupported. Also some of metric (network) can need root permissions - see resource 1.

Resources:
1.) gathering container metrics
http://blog.docker.com/2013/10/gathering-lxc-docker-containers-metrics/
2.) zabbix module docker (alpha release)
https://github.com/jangaraj/Zabbix-Docker-Monitoring
3.) google go implementation of container monitoring
https://github.com/google/cadvisor