Infrastructure is definitely required - safe bikelanes are almost a "must have". I live on the highest point in copenhagen and bike to the lowest. Granted it's not a mountain. Weatherwise, and I bike to work every day - 6-7 km btw, the summer is great, fall is lots of rainy days (but having quality rain clothes helps). In the winter, which granted is mild - but goes down to maybe -10c, you can still bike, even in heavy snow and when the bikelanes haven't been cleared.
I love biking - taking the car would be horrible, especially parking wise, and the public transportation, while good and regular is just not for me.
And I'd like to clarify: Safe bike lanes mean you are comfortable riding a bike while transporting your 3-year-old in a trailer behind it. This is the sort of safety that is required.
> If it's -15C and sunny it's good, but if it's +15C and raining it's a pain.
In the Netherlands and I think even in Copenhagen, 15C and raining is much more common. In my own experience, raining isn't the biggest pain. I hated the wind the most.
I love biking - taking the car would be horrible, especially parking wise, and the public transportation, while good and regular is just not for me.