Just a quick hint for all the commandline-jockeys: The standard-encoding for new MySQL-Databases on OS X Server 10.5.X is not UTF-8 but latin1.
Do not forget to specify the encoding when creating a new database, seriously. I suspect, that this depends on the language the system is installed in. The system that tricked me was using english, naturally. 
It didn’t help much, that WordPress thought writing to a databases using UTF-8 encoding. Everything worked fine until I dumped the database and restored it on another system.
Alternatively, there is no my.cnf in the standard-locations on a clean OS X Server 10.5.X install, create one and specify the right encoding there. But get in the habit of checking the current default encoding before creating a new database.
Just a quick FYI.