Poultry Deworming and Vaccines question

I'm sure this question has been posed, but couldn't find it anywhere. I'm curious how many folks with small, backyard flocks (less then 15-20 or so) follow a deworming and vaccination program? If so, what do you use, and when? If you don't, have you had any problems?

Deworm spring and late fall.
Ivermectin of you want to blast them or diatomaceous earth in their feed if you want to go natural.
You don't need to vaccinate unless you are showing or have a disease problem in your area.