I think most users expect Netflix to be up 100% of the time, in an effort to make sure that is possible Netflix has implemented a rather extreme approach to making sure its happy that it can handle server errors.

They've implemented what is called a Choas Monkey. This will randomly throw a tantrum in their system and they will see how it affects performance as well as other stuff like security.

The article is a bit technical but a good read and they are very open with the results.