actually there's a difference if you use unibody or the pre model.
i use tab to click with my unibody,
but the older model I do the same as well except you will always have your thumb ready on the button.
but with unibody, full trackpad you really do get more space and usually no using thumb at all.
In the beginning I stil have my thumb on it and navigate with index finger
the trackpad will works fine, eventually with only 1 finger and easier for me.
Also bit scare off by a topic here with crack on trackpad so I never use button.