Damn, you just reminded me that this is something I have postponed forever... I think the reason is simply that it's so frustrating to feel like a beginner again, although my times and stroke count are in the same ballpark whether I breathe left or right.
I'm currently training for my first half Ironman, and should definitely learn to breathe on my other side.
Any advice on how to make it easier? Should I simply force myself to breathe on the left every other lap?