Most of the experienced players here have their shield button mapped to left mouse click already, but I think it would be easier for noobs to learn how to shield properly if it was on left mouse at the beginning.
I bet a lot of noobs don't know how important it is to use their shield frequently because it's positioned on the awkward X button.
I have my shield on my right-click and attack on my left! What does that make me?!?! D: