The Ceilometer project was started 6 months ago on the realisation that all public cloud provider wanting to use OpenStack would need to rewrite exactly the same code to properly meter the use of their infrastructure. Ceilometer stated goal is not to provide a full billing solution. It deliberately limits itself to the first phase: collecting the information needed to establish billing lines.
The project description states:
"Ceilometer aims to deliver a unique point of contact for billing systems to aquire all counters they need to establish customer billing