Newer Apple hardware has touchpads where the entire touchpad is the button.  With the synaptics driver, drag and drop is very awkward and sometimes impossible if the drag distance is large, as I must drag with the same finger that is pressing the button.  If I hit the edge of the touchpad and need to go farther, I cannot lift my dragging finger to move it to the other side of the touchpad, as that will also release the button and end the drag.

MacOS X handles this very well -- you can click and hold with one finger, and then drag using another finger while keeping the click finger in one place.  Unless I'm missing something, I'm unable to enable similar functionality using the synaptics driver.  This type of behavior would be great as I'm not a fan of the 'tap lock' method (which I believe synaptics does support).

On a side note, this behavior is also useful for pop up menus.  You can click and hold with one finger, and swipe vertically with another finger to select the menu item, then release the first finger to activate.  I just can't make myself get used to the click-release-navigate-click-release-activate method of menu navigation.