At the moment I am home sick and being unable to rest, I passed the time by rereading the rulebooks for TI3 and both of it's expansions. As I'm reading a random page in the Shattered Empire booklet, I come a cross a small rule update on retreating (now called Tactical Retreating) that I must have missed.

If I realized this rule before, my games would have gone differently I can imagine! Doh!

Racial abilities and all techs are super easy to forget and/or overlook in my experience.

A couple that I've dealt with or seen players who were unaware of:

Trade goods can't be spent as influence to increase your votes during political/assembly.

When using the alternate strategy cards from SE, add another objective card during set up.