From PDF to MP3: Motivations for creating derivative works
by John Hilton III.
First Monday, Volume 14, Number 9 - 7 September 2009

From the conclusion:

This study indicates that individuals are willing to create derivatives because they want to help others access a given work and they want to make it more convenient to access it personally. Some derivatives, such as changing file formats, can take little time to create. Other derivatives, such as language translations, can be extremely time–consuming. However, individuals are willing to voluntarily create both types of derivatives. Nearly all those surveyed indicated they were glad that they had created derivative works, feeling like they were part of a community effort to share a given work with others. These creators of derivatives believe that as the awareness of open licenses increases others will be encouraged to create derivative works.

The study is fairly limited -- only 17 people were interviewed, and the original works were all books on the subject area -- but it's interesting nevertheless since it focusses on the motivations of people who do relatively uncreative mundane work, but still enjoy doing it because a sense of identity this creates.