Impressive list of features. Does anyone know if HAProxy is used by any IAAS/PAAS providers?
It's not necessarily part of OpenStack, but you'll most likely find it in every openstack deployment out there.
We use it quite extensively for Rackspace's Cloudfiles (Openstack Swift). I discuss it a bit in this talk: https://www.youtube.com/watch?v=YxnFUQHIwNs