You know, I wish they would replace this feature with a second button that would lock and hold the automatic settings until released. Holding the button with just enough force till the right moment is a pain!

Which is exactly how you can configure Canon DSLRs to work. You can also separate out focus lock from auto exposure lock as well. Very handy when recomposing shots after fixing the focus or exposure.

P.S. you can't do this on the Canon D300/Digital Rebel, it was one of the features from the Canon 10D that they dumbed down