Thanks for mentioning this. I had found the documentation page you linked above, and I wondered why there wasn't a reference to .FormatDate()
How would you grade arcpy documentation overall? While I'm learning more and more about python I anticipate some head scratching along the way, which is of course minimized by good documentation. However, I didn't anticipate struggling so much to find this particular solution, after all finding DatePart('yyyy',[DateField]) is so much easier. I'm interested to hear the opinion of someone experienced.