In stores that have them I use the self check ones. The Neighborhood Wal-mart(think mostly groceries and a few self-hygene products on my way how has half self check out and half regular check outs. I go shopping once or twice a week so I usually don't have that much to check out. And because I worked in a retail job for so long I can check,pay, and bag my stuff appropriately a lot faster than a checker can. I can get roughly 15-20 items including produce scanned,bagged and paid for in 3-5 minutes.
So it's a great time saver being able to do a bunch of shopping in and out of the store in like 10 minutes. But I never really considered the whole "taking a job away from a clerk" thing. So I guess if there's time I'll let a clerk do it. But selfscanners are just so cool and it's fun to me. I race people in the other lanes sometimes to see if I can get my stuff done first.
Nothing more fun than getting in line after some soccer mom with half the items getting it done and paid for before she gets close to being done.