Listen for yourself, use foobar and do an ABX test between 320 and 192, assuming you have the lossless file that you can transcode from.
I think that hearing is very specific for each person, just like how vision is.
Like if you were to ask to a group of people "can you read that other there?" 15 meters ahead, everyone is going to give you a different answer.
Hearing is the same, it's just that hearing is not as prominent compared to vision, where bad vision usually requires aids like glasses, contacts and surgery, hearing does not require such unless you have a severe case of hearing loss or a disorder.
And besides that, some people just have a "knack" for hearing the subtle nuances in music, experience aside.
Personally I'm in the camp where I can hear some difference between 128 kbps and lossless on songs that I'm familiar with, 192+ is unsure for me, very song dependant, and the higher it goes, the finer the line (as it should be).
I think that the mp3 encoders nowadays are very good, even 128 kbps files are very much listenable.
But even so, I'm not gonna say that there is no difference between 192 kbps and lossless.
To go back to the earlier analogy, that's like having a near-sighted guy doing an eye test; just because he scores bad doesn't mean everyone else will.
Your ears, your hearing, so form your own opinion about it.