As predictable as the sun, the iPhone home-button will start failing eventually. My dear friend had her button start giving her troubles a week or two ago, but got by with the new virtual home button in iOS 5. When I told her I could fix the phone for her so that she could wait for the new iPhone 5 before upgrading she was very excited!
The repair instructions are great and easy to follow. There are two pictures that shows the three screws for the screen assembly on the side of the phone bezel - I mixed up the sides, but this did not really matter. The full repair took about an hour as I was extra careful (my friend sat next to me, biting her nails and looking at me in horror as her phone was stripped down to parts one screw at a time), but in the end, the result was great!
Have a good system for how to store the screws and pieces that are removed in the right order. Especially for the steps with multiple screw sizes in one.
Also, make sure you have a magnetic screwdriver, (or can attach a strong magnet to your screwdriver in order to "magnetize it", as the biggest challenge is to remove the screws once they are loose, or to fit them back into the holes before tightening them again.