Erm... I wear three at times (ducks). Much of my stuff is in cold places and I have cold feet. I use a thick pair and a medium pair, and quite often a liner pair - thicker in winter, thinner in summer. Suits me well and is very comfortable. But if I was to purchase a new pair of boots for summer use, I'd go for a thick pair and a liner. In fact I did this last year, a pair of goretex fabric/leather boots for my Balkans cycling/walking trip. Worked fine, and suprisingly accomodating with just a thin liner pair or even two pairs of thicker socks in the cooler eves. Wouldn't walk with two thick pairs in them tho.