Mozilla Metrics has created a five node ElasticSearch cluster on some test machines that is using the Twitter River functionality to automatically retrieve a filtered set of documents from Twitter's streaming API and index them.
I've just created this page to document the first sample query:
https://wiki.mozilla.org/Army_of_Awesome/ElasticSearch_Prototype
I would love to get some feedback from the ES community on points/questions made on that page and improvements / ideas for the query.