Our local Home Depots started trying them out a few months ago. I was an early-adopter, so I usually had them to myself. Now everyone is using them so there are lines. Obviously, HD is gonna put more in since it's been so successful.
If people can self-scan all types/size/weights of hardware goods, they can certainly scan grocery items. Obviously, grocery store mgmt has been getting market G2 on this activity (as well as experiencing it themselves on a Sat morning after doing their own HD run).
As some other posters have pointed out, this is the end of the union and the existing checking/bagging business model.