How to have a combined search view that shows both users and content on search terms?
Haven't tried it, but I believe you could use Apache Solr with the http://drupal.org/project/search_api, http://drupal.org/project/search_api_solr, and http://drupal.org/project/search_api_multi

Create two indexes, one for nodes and one for users.  Then create a view that uses both indexes.