I remember my first VBR MP3. It was an Xing encode of a Black Sabbath tune, whch varied from around 80kbps to 160kbps. There was bad distortion at every rate which seemed to change incoherently with every visual switch of bitrate on WinAMP.
Since I never use Xing, I'm still not sure to this day whether it was a bug in the then-current version of WinAMP or the Xing encoder's true colours showing through.
Now I love VBR MP3. I try and use --aps as much as possible with my RioVolt SP 250.