I buy alcohol at self checkout sometimes. However, I'm always quick to offer my ID to the overseer. Our self-checkouts usually have one person for like 6 lanes. It's so much quicker at self checkout if you only have an item or two. However, later at night, when the manned registers are open, I'll go there and let someone else bag my groceries.
The one problem for self checkout, is like MAF said. They treat it like a goddamn calculus problem. I will avoid any self checkout where the person is above 40. At that age, it's too old for those guys to learn new tricks. Other than the fuckers who shouldn't use it, self checkout is the shit. It also gets a plus for being "too intimidating," usually leading to much shorter lines. If I'm getting more than about 10 items though, no way I go through self checkout.
The biggest problem, like in most other areas of society, is that there is no more fucking common courtesy.
