Headbutt, what a wonder it is <33. I particularly didn't like it later in the game, where as a battle move it didn't do much to my opponents, but in the early game it was also a useful battle move with that extra flinch chance thrown in :D.
I loved this feature so much :333, it was definitely better than the Honey Tree one which I found tedious and a bit irritating at times, waiting. Never mastered how to do it XD;. It was so much simpler, just walk up to a tree and let your Pokemon do the magic :). The Pokemon you could get were brilliant, especially ones like Heracross and Natu, they made great team members :).
So I definitely loved the headbutt feature <3.