The mp32ogg ebuild should require mpg123 as a dependency becuase it is required to actually make .ogg's that aren't empty. It will run without it but all ogg's created will be empty and 4 kb.
Steps to Reproduce:
1. emerge mp32ogg on a system without mpg123
2. use mp32ogg
It produced empty .ogg files
Succesfully converted mp3 files
Yep, the perl script relies on /usr/bin/mpg123. The fix is now in portage.
It appears to be fine now. Thanks for the swift resolution.