We use blueflood developed by Rackspace at Square which uses cassandra , coupled with a query layer called MQE (https://github.com/square/metrics). While it's actively developed, I definitely recommend taking a look if you are interested in highly scalable metrics system with decent strategy for rollups. (100k+ metrics/sec).
The reason we think InfluxDB is compelling as a standalone server is that you can get 300k metrics/sec on a single server. The scale is there for many use cases in the current release
