I did this early on a Saturday morning in August 2008 and there was quite a lot of traffic, as the climb is on a main road from Tuscany into Emilia-Romagna. There is a demanding central section, shown on the diagram here as from kilometres 7 to 11. As we all know, when you are going slowly the traffic seems to intrude more! This is the main drawback. Otherwise the road surface is good and the scenery spectacular. This part of northern Tuscany (Lunigiana)is like a mini-Alps, with a number of good climbs into the Alpi Apuane and the Appenini. When you get to the hotel at the top you can turn right (coming from the Tuscany side) and after another 3 km reach the ski resort of Cerreto Laghi. This is an easier section and makes for a faster finish. I think the whole Lunigiana region is a bit of an undiscovered cyclists paradise (Italian cyclists know it well, mind you). Perhaps not on the scale of the Alps, but with great compensations in the food, the friendliness and homeliness of the place.