To enable tap-to-click for Synaptic touchpads (including BCM5974 in MacBook Pro) for Debian Wheezy:
su
mkdir /etc/X11/xorg.conf.d
cp /usr/share/X11/xorg.conf.d/50-synaptics.conf /etc/X11/xorg.conf.d/
nano /etc/X11/xorg.conf.d/50-synaptics.conf
Section "InputClass"
...
Driver "Synaptics"
...
option "TapButton1" "1"
...
Restart X.