When to batch and when to queue?
I was building a Drupal 7 module and needed to implement a way to import/sync thousands of nodes, files and terms through a SOAP connection. The manual sync can be accomplished in the UI using the excellent batch API (example) which was also available in Drupal 6. But when do you use the new queue API in D7? Short answer: when you need to perform large processes through cron. See also the DrupalCon SF video comparing the two methods.