Here's what you need to do:
- Open any application (I picked Mail)
- Hold down the power button on top of your phone until the Power Off slider appears
- Release the power button (don't hit the slider though)
- Now lightly hold your home button until the icons view of your phone reappears (This may take a while, just keep holding the button lightly with constant pressure)
- Once you are returned to your icons screen you're done
The blog post I linked to above explains that this is how the home button is re-calibrated. Through normal use the phone may get out of synch with what a normal press of the Home button should feel like. This should correct the problem for most of you.