A family member gave us their iPhone 4 after they had upgraded to an iPhone 4S. The phone was great, but the home key was warn out. I jumped online, did a search for 'iPhone 4 Home key how to fix' and iFixit popped up.
The repair went well, took about an hour. I would take someone who has done it before much less time. I really read the instructions well and just took my time.
When re-assembling step 30, really take care here to make sure the cables are all the way through. Also some more detailed pics of connecting the home key (Step 32) would be great. I actually found it easier to connect the home key cable when the front screen was back on.