Asynchronous programming FTW!
Source: YAPC::EU 2012 on the 2012-08-20.
First Sawyer tries to help one of his family members to pick a movie, and then writes down the algorithm using WWW::Mechanize.
Then he explains what are callbacks and shows code how WWW::Mechanize would work if it allowed asynchronous operations.
Then he shows Juno a testing library that works in an asynchornous way and Algotighm::Diff::Callback which is an asynchronous version of Algotighm::Diff to compare two data structures. Giving you the control via callbacks.
Explaining what Asynchronous programming - just and event loop.
Also check out WWW::xkcd.