I actually never sterilized my son's bottles (boiling in a pot of water or microwave bags).
I would soak his bottles in hot soapy water in the sink, wash them with a bottle brush, and hang them to dry on the bottle rack. He has never been really sick (just the odd cold), but nothing compared to some kids who parents were anal about sterilizing.
I am also one of those moms who...
- if his bottle drops on the floor I clean it off with whatever I have handy (baby wipe, wet cloth, my clothes)
- right from when we came home from the hospital I never heated up his bottles, and always had about 10 waiting in the fridge; mostly he would just drink them right from the fridge, and who has time to make bottle by demand when you have a newborn.
His immune system is great, and the first year was a breeze.