My iPhone 4 was about a year old when the home button started to get flakey. Over time it got to the point that it just plain didn't work anymore. I was using the workaround that uses the accessibility menu to get an on screen home button but that was annoying. I figured I had a 50% chance of changing the thing and having a working phone - this is fairly complex and requires dismantling a lot of the phone to get the old button out. But if I didn't try I'd have to buy a whole new phone (Apple doesn't change just the home button - they make you junk the device and buy a new one!) anyway.
Took about two hours, start to finish. The printed screw chart from the guide is a big help - there are a lot of screws of varying size to keep track of. As luck would have it I dropped one when I was almost done, so I had to order a replacement screw set. At least when that comes I can put it in without dismantling that much of the phone... and the phone seems to work well enough without it.
I recommend using an old New York City Transit Metrocard instead of an opening tool to split the front panel from the metal frame. In fact, they work well to open all sorts of things. I know the transit pass in Chicago is a similar thickness but the texture is a bit different, so I don't know if they work as well - probably there are other transit passes that work for this. But living near New York city I have a nice supply of the NYC version.