I get slightly numb big toes on occasion. It usually happens when I've been walking downhill for a few hours. When I take my boots off, the bottom of my big toes will be slightly white and numb. My toes aren't hitting the front of the boots or anything; I think the big toes just aren't used to the cyclic walking pressures, since I don't walk 15 miles every day. It always gets better in a few hours.
I've actually been able to prevent this from happening by putting moleskin on the bottom of my big toes. But keeping moleskin on the bottom of toes is harder then it sounds, and numb-toes is more of a curiosity to me then a nuisance (at least when frostbite isn't a concern).
I've also gotten numb-toes while cycling in the winter. When I would get home after doing that, I would have excruciating pain when the toes regained feeling. Fortunately, no toes ever turned black. So, if my toes go numb in the winter, I am more attentive to them now.