[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
Edit the below file, with this command on Terminal.app:
sudo vim /Applications/XAMPP/xamppfiles/mysql/scripts/ctl.sh
On line #59, delete this:
/Applications/XAMPP/xamppfiles/xampp startmysql > /dev/null &
and put this
/Applications/XAMPP/xamppfiles/bin/mysql.server start > /dev/null &
(save the file: ESC :wq!)
Restart All Servers on XAMPP.app (manager-osx)