I have been using the Drupal Apache Solr module since about May 2008 and have seen it evolve into a awsome feature rich module. It is now in a state that it is able to do most of the standard things you need for a client build out of the box including field boosting, more like this and faceted search. The only things I always ended up adding patches for was returning custom fields (to the fl "field list" param) and messing with the results returned from Solr e.g.
