Here is my personal strong opinion on the matter:

1/ I put a license at the top of every source file. If the file is distributed outside the project by accident, it is clear the copyright and license status.

2/ I put the full license and all copyright authors in the `README` file consistently, e.g. https://github.com/ioquatix/rubydns - I also expect all contributors to add themselves but most don't. Specifically, I try to make sure the files the edit have their name in them.

3/ I don't have any additional files like `LICENSE` or `AUTHORS` because I think they require one extra step to read, and the MIT license fits nicely at the end of the `README`. I would also stay away from `AUTHORS.txt` - not sure if there is any real point in this, it certainly no bearing on copyright/license.

I like simplicity. Having the copyright and license in the README keeps things simple IMHO. YMMV.