about: ElasticSearch's new "Percolator" feature, which enabled to index queries and find which documents match them : instead of sending docs, indexing them, and then running queries, one sends queries, registers them, and then sends docs and finds out which queries match that doc.
about: A distributed, highly available and restful search engine. It looks very promising and rather easy to deploy and have working. The killer feature : schema-less indexing (auto-discovery based on conventions). A serious concurrent to Solr ?
about: An interesting article from Lucid Imagination employee Mark Miller about Scaling Solr. It gives a lot of good practices and tips on how to get the best out of one indexing machine, and explains how to use Solr built-in replication system.
about: Symfony Solr search plugin, which binds the Solr indexation / removal / search to Symfony events, and thus easily brings Solr search into Symfony projects. The (de-)indexation process could however be improved by overriding the save/delete model methods.