I'm going to Prague for a week and I'll be all day out in the cold and in the snow. I have a Canon 600D and I just discovered that my camera is not weatherproof. Is it safe for my camera? At the hotel, the temperature will be at least 20C, and outside not more than 5 maximum, so what am I supposed to do? Can I still use my camera?
Check the specs of your camera wrt temperature. If Canon says it'll be fine, bring a couple spare batteries because cold saps battery power.
As for the temperature difference between outside and inside, what you need to worry about is condensation on the camera + lens. This will occur whenever a much colder item is moved into a warmer environment. The solution is to put your camera inside an airtight bag (a double layer of Ziplocs should do) before you enter the warm environment. Wait until the temperature of the camera has reached room temperature before opening.
Think Tank Photo makes a product that protects your camera from the elements: