We still managed to have fun with it last year with the Epic Harvest Brewfestival Kodo Ride. When the holidays were overlapping, we turned our mounts into kodos and rode them to honor Grom Hellscream. The gallery is below. Don't adjust your sets; we were riding drunk. No, this was not a responsible ride on mythical animals in a fantasy world.
So go forth, eat your free food and honor your faction's harvest hero. And if you're into more compelling in-game holidays, don't fret: Pirates' Day and Brewfest are coming up within the week.
What do you think Blizzard should do to make Harvest Festival more interesting?
Disclaimer: This post is subject to change without notice if Blizzard actually implements a full-fledged holiday this year.