This link provides exhaustive details as well as points to others experiences:
Key points are:
Cause is unknown.
Cause is indeterminable due to the failure of the logging system.
Steps to Reproduce:
1. Install metalog on *some* ppc machines and wait
logins would freeze at authentication with both local and ssh logins. Also other
authentication related apps would fail like useradd and userdel or su.
unable to reproduce and i use metalog on every arch Gentoo supports
please re-open if you can reproduce with 0.8_rc1+ and you can track down the bug itself