I am unable to find how to get these menu fields to be active. I just purchased MarsEdit after the trial and thought it was a limitation. I have even went so far as to add a custom 'keyword' field which does not pull in the keywords. I used the info on post http://www.red-sweater.com/forums/discussion/comment/9089#Comment_9089
and verified there is a keyword being brought in from my blog. I'm using a self hosted Wordpress blog.