On tip: please don't use the tags that are pressed flat against the collar. I recently was at the shelter here evaluating a beautiful, friendly, well cared for white GSD. He had very thick fur. When I went to rub his neck, I felt a metal plate on the collar, and parted the fur to take a look. It was an ID tag that had been missed by both animal control and the shelter intake staff. The dog had been sitting in the shelter for 3 days, without the owner being called. His hold was up and he was ready for rescue, adoption, or euthanasia.
I called the owner with my cell phone right then. The dog was reclaimed the same day. It all worked out fine, but only because I happened to be volunteering that day and spent some time with that dog.
It's not that the staff doesn't try, but as busy as they are, things get missed. Dangling tags are easier to spot on thick-coated breeds. The whole point of tags is to get the dog home quickly if disaster strikes, and apparently, the flat-against-the-collar can be overlooked--it was something I'd never thought of, but now that i've seen it happen, I want big dangling tags on my dogs!