I compared this summer ogg vorbis to mp3pro VBR (codec bundled with CoolEdit 2), at the lower quality : -q0 for vorbis (-1 wasn't built in the first release of oggenc 1.0) and VBR qual-10 HQ for mp3pro.
I did ABX test on many samples (classical one, with a wide dynamic range, and not overcompressed sound) : mp3pro was clearly the winner at those low bitrates (under 64 kb/s : ogg -q0 turn around 50-55 with classical material). A winner, but of course, sound was really poor : distorsion, poor stereo, pre-echo. Vorbis add to this an electronic noise, clearly audible at low volume (frequent with classical music).
At higher bitrate (-q2, so 80 kb/s with classical), vorbis take the advantage, but difference is small. Over -q2, vorbis beat obviously mp3pro...
But it seems that with non-classical materiel, mp3pro is much closer to vorbis. Maybe under this one... I don't test the codec at low bitrate with metal or techno music.