5S launch day: stayed up until 3AM ET for the online orders. Got my order in. Went to sleep. Didn't sleep enough. Went to work. Left work. Pulled out 4S to read email.
Dropped 4S on sidewalk. Picked up. No cracks!
Hours later: solid crack.
Verizon trade-in estimate with no cracks: $200.
Same estimate, with crack: $76.
Spent $50 to replace the back before trading in, to make up $74.
Removed old back.
Installed new back.
Repair time: ~45s.
If it's not coming off, you need to slide it up a tad further. I bought a spudger for precisely this. It worked great.