Do you have a better sound system? Or a different one? I had a friend complain to me that my tracks sounded better than his, even though they were the same source, it was because of his sound system. Also, some sound cards (if you've updated drivers or changed sound output devices) will try and make MP3 playback sound 'better' through use of 'spacialization' or abience/echo or even specialized equalizer settings.
There's a ton of different players that could be affecting the perception of your music. Generally 192 VBR should be pretty good, but on a super-sound system I can usually tell the difference from that and 320 even with my old ears. It doesn't sound 'horrible' but you get the idea.
I've transferred my music collection through 6 hard drives now, the sound quality has remained the same (so has the file size) so something else is probably affecting the reproduction.
Thanks for the reply Obsidian...I actually figured it out and it was a glitch in Winamp that was reporting the wrong bit-rate but just for the cd's I'd ripped all those years ago, so there is still a mystery but at least I know there is nothing in my computer stealing the bit-rate from my rips!