i'm also one of those poor souls who installed mysql and DBD::mysql and encountered this error when running my perl apps:

dyld: lazy symbol binding failed: Symbol not found: _mysql_init
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after reading all of the posts here and elsewhere, and having no success, i decided that there must be some issue between how the mysql binary was compiled and how DBD::mysql was being compiled on my system. i happened upon Dan Benjamin's excellent howto for installing mysql from the source:

http://hivelogic.com/articles/view/installing-mysql-on-mac-os-x
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following his instructions very carefully and then re-installing DBD::mysql solved all of my problems.

i think part of my issue may have been that other software packages i've installed have required the environment variable:

ARCHFLAGS="-arch i386 -arch x86_64"
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and this may cause some inconsistencies that are solved by compiling the mysql source. as noted by the archflags i'm running an intel mac with leopard but i believe this solution works for earlier versions of os x.

the only problem with this approach is that i lose the preference pane that allows me to stop and start mysql thru the preference panel. it must be done manually on the command line. oh well, i'd rather be able to run my perl apps.