Having only owned these for a week I can't comment on their durability but I thought I would offer my first impressions for those considering buying these socks.

First, the fiber content listed on Amazon is completely wrong.  The socks are an even polyester/cotton blend with appropriate amounts of spandex for stretch.  There are two distinct knits used in the sock which gives them a feel half way between a full-on dress sock and casual/athletic sock.  A flat knit is used for the upper portion of the sock, very similar in thickness/feel of a dress sock.  The sole and ankle have a thicker terry-like knit consistent with a pair of athletic socks... but not as thick as an athletic sock.

The combination of knits offers a great balance between low bulk in the calf area and a bit of extra padding for the sole and ankle.  The different knits are not visible from the outside of the sock.  The overall look is 'dress casual' and would go great with loafers or other casual shoe. They are a little too casual to be paired with your best dress shoes but would do in a pinch, keeping in mind the padding in the sole/ankle area will make them thicker than your regular dress sock and possibly making your shoes too tight if the shoe fits 'like a glove'.