Here are a few production users: https://cwiki.apache.org/confluence/display/SAMZA/Powered+By
The Metamarkets team wrote a nice post on their use of Samza a few days ago: https://metamarkets.com/2015/simplicity-stability-and-transp...
The Metamarkets team wrote a nice post on their use of Samza a few days ago: https://metamarkets.com/2015/simplicity-stability-and-transp...
Or may be they did not transition and are actually using both, I don't know