There was a long article in the New Yorker magazine a few weeks ago about the resurgance of mules now - giving a lot of their history, talk about their good attributes, comments on various difficulties, how much they need to be trained and how good they can be if trained. Some are even being used in dressage now, since some think they are smarter than horses. I can't quote the whole thing, and it is only available if you are not a subscriber by paying a fee (not sure how much, possibly something like $2.50). This might be available at your local library.
The abstract (general idea of the article) is here:
http://www.newyorker.com/reporting/2010/02/15/100215fa_fact_orlean
I at least take from this that training JJ is very important, Arella Mae. If you don't get ahold of this article, you might want to look into recent books about training mules - even if you have a trainer, you might want to read up yourself.