We are! And unsurprising it's a great fit given k8s is inspired by Borg and Prometheus is inspired by Borgmon.

There's a few, here's a recent talk by Weave for example: http://www.slideshare.net/weaveworks/kubernetes-and-promethe...

Here is the CoreOS blog on using it: https://coreos.com/blog/prometheus-and-kubernetes-up-and-run...

Yes, it works wonderfully. I published a Grafana dashboard for this here - https://grafana.net/dashboards/162