Power switch on sister's iPhone 4 quit working a long time ago. Didn't depress or click at all. Battery would wear down quickly waiting for the screen to time out and go to sleep, and things would sometimes bog down without the ability to reboot the phone.
Repair worked like a charm. Took longer than expected. Lost one redundant screw (of the two holding the power switch to the case). Found it particularly challenging folding the new power cable in and around the other cables and had to try several things to get grounding piece by camera to sit still while reassembling. Also took a minute to figure out that the blue tabs on the new part covered adhesive on back. But in the end the phone went back together and everything works great and my sister is really happy to be able to use that button now.
After dry-fitting logic board in place, use tweezers to insert grounding piece by camera underneath screw hole in logic board. Then put that screw through the logic board first, to holding grounding piece in place. Watch that the grounding piece doesn't get smashed under the camera when putting the camera back in.