A little under 150 million documents. We are indexing topics (not a big
dataset), most of the dataset.
10 servers, moving to 15 soon, 20 shards, a little over 1tb of indexed but
that number should increase soon.
On the website we are not doing very complicated searches at this time. On
our internal tool for Klout Perks we have pretty complicated searches based
on a bunch of criterias like different values generated by our algorithms
associated with each user, topics, geo location, etc. We also do some data
exports using scrolling searches, mgets, etc. We should be adding more
criterias to the public website sometime soon as well.
The internal tool has been using ElasticSearch for a while, it powers most
of the eligiblity checks for Klout Perks but the public facing search has
just been released recently.
Hope that clarifies some of your questions.