After a few months, my iPhone 4 button just stopped working all the time. You'd have to press it really hard, or press it a few times, to get it to register.
Everything went exactly as it should have. It took about an hour to follow the install guide and replace the button, and about 20 mins to put the phone back together.
Be careful putting the rear camera back in, if it's not in correctly the back cover won't go on.