It's not as hard as you think! And, for me, it's both inherently fun and better than the alternatives (driving or transit) Sure I save money and whatever, but at heart I do it because I like it. Attitude is important - I used to not ride below about freezing, but since I lived in Michigan at the time this meant little to no riding for months, and I eventually decided that it sucked more to not ride for three months than it did to ride in the cold, so I learned to like it - I already had the clothing, so all I needed was an attitude adjustment.
Tire choice is important. The three-season tires on my primary bike are terrible if there is anything vaguely slushy on the ground, so I replace them with something else. The tires on my single speed are perfectly fine year-round. I live in Chicago where the major streets tend to get squeegeed curb-to-curb and salted generously every time it snows. Tires with a positive tread can be helpful if you have an irregular surface or there is some accumulation. Studs are wonderful for ice, but not needed for anything else (the positive tread will help, though)
I have never had a problem staying warm - after, say, the 50-minute ride from my office to my girlfriend's home I find it difficult to avoid being sweaty, no matter how cold it is - except for my hands, which are viciously cold. Pogies were my miracle - now I can keep even my hands warm in -10F temps.