[EDIT] The last version of MAMP with the last version of OSX Yosemite works fine.
I installed the beta of Yosemite two month ago, no problem with MAMP. With the last
You can also try this workaround posted at http://community.bitnami.com/t/mysqld-doesnt-start-in-mac-os-yosemite/25153
/Applications/XAMPP/xamppfiles/xampp
Look for:
$XAMPP_ROOT/bin/mysql.server start > /dev/null &
And add unset DYLD_LIBRARY_PATH on top of it. It should look like:
unset DYLD_LIBRARY_PATH
$XAMPP_ROOT/bin/mysql.server start > /dev/null &
I hope it helps