Michael O'Leary biggest mistake
Michael O'Leary biggest mistake was to ignore the Danish "Jante Lov" (unwritten law about how to behave among Danes).
The law is described in the link provided by justinabeavor, but to sum it up its all about being humble and being able to access how things are done in a new place once you get there, rather then just stumbling in trying to change the way things are done. Michael O'Leary failed miserably....
When in Rome do like the Romans, and when in Denmark do like the Danes!
Denmark is a well organized country, and luckily we can afford living without having to live by Michael O'Leary rules. He won't be missed.
Last but not least, the outcome of this dispute might end up being the beginning of the end for the Ryanair way of doing business. Other unions in other EU countries are also looking into the options used by the danish unions.