Entities are a new and exciting concept in Drupal 7 and a few modules are starting to make use of them. A co-worker (Scott) of mine has recently jumped on the Drupal bandwagon. He's been reading up on the Drupal development books and creating custom modules. A new module that he was working on created a new entity type. Great! Not a problem, the Drupal books and online docs provided pretty detailed steps. We ran into a wall however when we attempted to theme it. The documentation was lacking at this point and looking over contrib modules that created entities didn't provide any entity theming examples.
Scott started digging through the code and eventually figured out how to accomplish custom entity theming. Even better, he contributed his findings to the Drupal online documentation. Win Win!
You can learn more about the solution he found on his blog post. Just don't give him too hard of a time about his blog running on Wordpress. :-)
Note: I closed comments on my blog post here... head on over to Scott's to leave any feedback.