I hated them and inwardly rolled my eyes at the SoCal girls who wore them with mini skirts in 70* weather. (Sorry Spartana!)
Now that I live in a place with real winters (days with highs that never break 30*F), I live in them. Mine are not real Uggs but the cheap knockoffs from Costco. Nothing is warmer. I have a pair of shoes by some fancy brand, made for snow and winter, and they aren't nearly as warm. If it is slushy out I leave he Uggs at home, or if I am being a tourist and going to be walking for hours, but otherwise, it is the Uggs. So warm. Even when there is snow on the ground, unless I am going to be wading through it, they are fine. I spayed them with a water resistant spray and sidewalks and parking lots are generally plowed, shoveled, and/or salted. I have 3 pairs thanks to a mom who keeps buying and sending, but I primarily wear 2 of them and one is 4 years old and in great shape. IIRC, mom said she paid ~$50. So I assume they aren't real sheepskin, but they are so very, very warm.
They have nothing to do with fashion and everything to do with function. I need Warm and I've yet to find anything as warm, even at double the price, or more.
I will say that they stretch a lot. A lot. They should be significantly tight when you buy them or else they will stretch too much and be too big. That's why so many people walk funny and make a clopping sound when they wear them--they've stretched and become too big.