isnt that the AE lock/focus lock for one shot mode/flash exposure reading test for flash photography button?  If so - yes i do use it occasionally - although i tend to shift the focus point instead as i find the only real use of the * is to aid in composition of an offcenteredly focused shot.

"In every colour, there's the light.
In every stone sleeps a crystal.
Remember the Shaman, when he used to say:
Man is the dream of the Dolphin"

Rich Meadows Photography