Some of the most enjoyable Drupal moments for me was the time I spent in 2009 testing Acquia's Search for Drupal. Acquia Search is a plug-and-play service within the Acquia Network, built on Apache Solr and available for any Drupal 6 site.
I think Acquia Search is probably one of the most significant services provided on the Acquia Network and the feature that will continue to attract businesses to not only Acquia but also Drupal. So although I'm no longer on the Acquia network, I'm pleased to hear that new features have been added to this Apache Solr implementation.
Some of the more significant features being added to Acquia Search include:
- Attachment Indexing - Utilizing the Apache Solr Attachment module you can now search the text in document files such as PDF and Word documents. This is big! Even cooler, those documents can searched locally or remotely.
- Multi-site Searches - Search multiple Drupal sites at once.
- Update to Solr 1.4.1 which fixes a number of bugs.
- Wildcard Searches
So I think obviously think Acquia Search is one of the coolest services ever provided by Acquia. Now, if you're a small time guy like me that can't realize the cost benefit to subscribing to the Acquia Network or your own Apache Solr implementation, you still have options.
Check out Chris Pliaka's implementation of the Search Lucene module. For smaller sites, implementing an Apache Lucene solution is a good alternative to using Solr, but I'd be hard pressed to recommend Lucene over Solr for larger and busier sites.