"They" say you should sterilise for the first 12 months. We have no particular reason as to why we sterlise DD's spoons - they just get chucked in the utensil drawer anyway! I don't put them through the dishwasher because I noticed one of them deteriated a bit. We will sterlise her bottles for the first 12 months (she is formula fed).
Thermometers - are you talking about ones to take bubs temp? I would not recomend sterlising a mercury one in a steam steriliser. If you are worried about germs, you can clean them with alcohol wipes. If you have one for the ear - you can buy covers for them that you dispose of after each use.

HTH

MG