In doubtful things, liberty; in essential things, unity; in all things, charity.
"In necessariis unitas, in non-necessariis (or, dubiis) libertas, in utrisque (or, omnibus) caritas." (Questionable attribution, see http://ccat.sas.upenn.edu/jod/augustine/quote.html)

A pastor who was catechizing his flock regarding a shift to celebration of the Mass ad orientem used this phrase in his bulletin letter (which was then cited on Fr. Z's blog where I found it today), and I'm glad he did cite it, because this is exactly what I was trying to think of the other day.  Sometimes mommy-brain gets in the way of recollection, but this is what I was trying to remember when I read some of the commentary posted beneath the English Mass colloquium video.  (This is one of those I posted on YouTube on the "catholicsacredmusic" channel, and occasionally one of the contributors to the New Liturgical Movement, Jeffrey Tucker, will post one of the videos and then it becomes a topic of commentary.  Because it was in English, it attracted more attention than some of the other clips he posted... a lot of it negative... and there were some comments questioning the choices of Fr. Skeris in the way he did the incense, when he had people sit for the Kyrie, etc. 

At the crux of it is the fact that in the Ordinary Form, there is more room for interpretation and some things aren't written or leave options open.  In other words, they are doubtful, so in that case the old maxim above calls for liberty.  I would also say those things mentioned in the comments are not essential (I would consider essential being the words of consecration).  As for charity, well we could always use more of that.