According to https://bugs.launchpad.net/ubuntu/+source/linux/+bug/441013/comments/5:
The behavior in realease Karmic has changed. You will be able to try it on a live cd and install tommorow. "Enable mouse clicks with touchpad" is now enabled by default. It has had this behavior since RC build.
According to https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/441013/ comments/ 5:
The behavior in realease Karmic has changed. You will be able to try it on a live cd and install tommorow. "Enable mouse clicks with touchpad" is now enabled by default. It has had this behavior since RC build.