Margaret Heller (Digital Services Librarian, Loyola University) has written a brief introduction to creating custom themes in Omeka 2.0 on the ACRL TechConnect blog. For libraries that already have Omeka installed, have access to the code, and have multiple groups requesting Omeka sites, creating a theme template can be a useful way to scale what your library can offer while adding a customized touch. As Heller notes, it can also be a valuable learning experience beyond working with the popular tool:
Since this was a new content management system to me, I still have a lot to learn about the best ways to do certain things. This experience was helpful not just in learning Omeka, but also as a small-scale test of planning a new theme for our entire library website, which runs on Drupal.