Ansible is great for easily provisioning systems and whole clusters. Compared to Salt it may be slower, but on the other hand it doesn't have to install "minion-like" software on the hosts it operates on. My very-near-future plan is to create an Ansible playbook for fast-provisioning Ceph clusters and automatically running a series of functionality tests on them. Also, I can see Ansible playing an important role on my efforts for automating virtualization testing.
This project is one of its kind!