I wear these socks nearly year round. I have worn Defeet wool socks for years and have always been happy with the performance. I will say, however, that wool socks typically don't last as long as nylon socks. The fibers will tear over time and create a hole.
I started out wearing Smartwool and while they are comfortable, they wore out quickly. I have worn some of my Defeet Woolerators hundreds of times and they take one heck of a beating. Of course, all the great things people say about wool are true and my long-time fight with athlete's foot was won by them as well.
I use these socks for cycling 34 of the year. They breath very well and they feel much better to me than the non wool socks. They are pretty thin, but they have lasted for years. The biggest problem that I have with them is that my sons keep trying to steal them from me.
I have several pair of DeFeet wool socks, some of which are several years old. I wear wool socks all year long, lighter weight in the summer and heavier in the winter. The comfort and durability of DeFeet socks makes them well worth the money.
These have been my go-to cycling socks for some time now. Very comfortable, warm on cool days and cool on warm days. They even maintain much of their warmth when wet. Initial reaction when I first received them was that they are not very stretchy. However, I believe this helps to keep them intact longer. I find that I am always wearing out the toe prematurely in stretchier socks such as SmartWool but less so with these. Pairs that I have had for over 2 years are still going strong. Added benefit, if I commute to work and forget my dress socks, I can use the understated grey without worry that they will look out of place.