I put together a little test to see how audible the differences between various bit rates are. It’s not the pinnacle of excellence in scientific methodology but it’ll tell us enough and makes good use of the tools the average person might have. If you’re interested in taking the test, it and everything you need to know about it are here.
The more responses I get, the better so please participate. If you post your response here, please post it on my site as well so I can tally it easily.