The home button of my iPhone4 have been working whenever it pleased to. So I figured it was either a dirty part or a faulty part. And the only way to find out was to disassemble the phone.
Fortunately it was only a problem of dirt. Also the place where the home button makes contact has a little plastic ring that I guess its used as an isolator. That ring wasn't correctly places around the contact area so I cleaned the thing and aligned the plastic ring along the contact circle.
Use the phillips screwdriver that comes with the liberation kit. I used for ALL the screws inside the iPhone. Well of course except for a flat head and the pentalobes. Other than that you are good to go.
Finding this out almost cost me one screw hehe.