I finally managed to get Drupal 7 work with MarsEdit and Blog API. Since I had a request to explain what I did, I have decided to include a summarised version of what was needed. Take note that I cannot give you a module that just works as the changes I had to make was quite specific to my installation. With some time and energy one can most probably make it generic, but I leave that to the reader.
First and foremost, the people at DITAinfo ported the core BlogAPI module that was removed from Drupal core, to Drupal 7. According to them it is working mostly, but for me it failed to work. In specific, the following functions did not work:
Posting a new entry - the categories and body did not show up.
Reading an entry - the body text and categories were not retrieved.
