I bought the back panel for the iPhone 4 via iFixIt. When it arrived I noticed two things: 1) The replacement part is lighter...
I followed the guide and it worked very well. However, after heating the glass for removal I found the lower right corner to be the easiest. Then I used an old credit card to separate the glass from the frame by sliding it around. The hardest part was installing the new LCD panel and glass because of dirt particles and fingerprints. Great tutorial and guide.
It is easier to start in one of the lower corners. The glass is not held by the rubber bushing.