I went to audio school and have done blind testing.

When I'm regularly keeping up with ear training exercises I can usually tell the difference between 128kbps and lossless with near-perfect accuracy, but 320kbps vs lossless I'm basically guessing. I still leave my projects and bounces at either 96/24 or 48/24, and all my downloaded music is in .flac or .wav, but I also am a pretty firm believer that unless you're actively training to hear the difference and using a very high quality setup the difference is negligible.