A couple days ago, Acquia moved Acquia Search out of beta and made it available commercially available through their Acquia Network service. Acquia Search is a hosted search service based on the Software as a Service (SaaS) model. The technology supporting Acquia Search is based on the the Open Source Lucene and Solr distributions from the Apache project. While a free search module is already available in Drupal, as well as Acquia Drupal, Acquia Search is significantly different and geared toward the enterprise. Smaller but high traffic websites would also benefit from Acquia Search.
CMS Report has been beta testing Acquia Search for the past four months and we've had nothing but a positive experience with the service. In fact I feel as a beta tester I somehow didn't do my job since I didn't have any issues to report to Acquia. However, Acquia did acquire various usage statistics, email exchanges, and surveys from us that they still benefited from CMSReport.com's participation in the beta program. Since I know only enough about Drupal to be dangerous, if I can't break it then Acquia must be on the right track with this product.