A friend sat down on a rock with his iPhone 3GS in his back pocket. Shattered the glass around the button.
It was simple, but tedious. I watched the video, then followed the step-by-step instructions. The hardest part was removing the glass from the plastic frame, and that because much of it was shards. I used a hair-dryer on low setting, and left my finger in the air stream with the glass. When my finger was just uncomfortable, I'd fidget with the fragments. Same thing to remove the adhesives after the glass was gone; spudger was REAL handy for that. After 90 minutes of disassembly and prep, it took all of 10 minutes or so to completely reassemble. Not one raven!
Despite the note in the instructions, I didn't even NOTICE the black tape on the side until completely disassembled. Also, despite the reminder in the instructions, I did ALMOST stick the ribbon cables under the glass. They are very stiff when new and resist all efforts to make them behave. Apply the heat to the GLASS, not the plastic. Remember to wear eye protection when dealing with glass removal, just in case it explodes. OH, and, keep the protective vinyl for the inside of the glass -- only remove it as needed for adhesion; then rip it off once the glass is firmly mounted (fingerprints are evil).