Solr 5.1 introduced a revolutionary Streaming API. With Solr 5.2, you get Streaming Expressions on top of it. Ever wondered on how to run nested queries in SOLR or running parallel computing capabilities, this could be the answer.
KnackForge has done a lot customizations on Drupal and SOLR integration. Earlier I wrote about Drupal-7-filtering-solr-results which covers limiting SOLR resutls. This is another work where we had to alter default apache solr autocomplete module to limit suggestions only to node titles. And other interesting challenge in it was to provide case insensitive search with case sensitive results and phrase based search.