two years ago i had my roof replaced. Ridge vents were installed as well as soffit vents. This fall I had the attic sealed and insulated. I've had about 3 foot of snow on my roof and no icicles as of last weekend due to the well ventilated and insulated attic.
Out of caution I raked all the snow off the first 2 feet of the roof last weekend because I was worried that a slow melt would cause water to build up on the upper part of the roof behind the snow on the lower part, although I don't know if that would in fact happen.