It is day two at Drupalcon Copenhagan, and Robert Douglass and I presented this afternoon on Apache Solr Search Mastery. While the concepts in this talk apply to the Drupal 6 versions, all the code examples are taken from the Drupal 7 port of the Apache Solr module.
Changes in the Drupal 7 version include wrapping all the data for the Solr query into the
$query object and transforming the CCK integration from 6.x-2.x into an integration with the Drupal 7 Field API. Of specific note there is that taxonomy data attached to a node is now a term reference field and so can be handled through the same general Field API handling as (for example) the fields provided by the Drupal 7 List module.
Attached is a PDF of all the slides from our talk together with James McKinney at Drupalcon SF. All the examples in that talk were taken from the Drupal 6 code, so is also a good resource for people developing Drupal 6 integrations. The video from Drupalcon SF is at archive.org.
More information about James' custom search paths for McGill can be seen in his blog post about it.