I sterilised Ashlea's bottles until she was 6 months, and after six months old she used sippa cups instead, which we just washed out.
The say now that there is no point to sterilizing bottles because as soon as you take them out and expose them to air, store them in the cupboard, touch them etc they are no longer sterile anyway. The only way they remain sterile is if you only use sterile tongs to handle them, and fill with boiled water and store in the fridge.
The other aspect, as was already mentioned, is that its actaully better for kids to be exposed to a degree of dirt and germs and it strengthens their immune system.
Another thing, alot of parents clean the kids dummy's by sucking on it. Fact is, there are more germs and bacteria in an adults mouth than on a filthy floor... Thats kind of gross isn't it???