Paul and I each have a Samsung Galaxy S4. His has been running Cyanogenmod, and mine is still on the stock ROM it came with. There are a couple of reasons that I hadn't upgraded my phone to CM yet, one of which is the fact that when we'd set up Paul's phone, we'd had to run through several nightly builds until we found one that actually worked on his phone. I figured that a final stable build would be available soon, and I'd flash to that when it was ready.
Yesterday while we were out at lunch, Paul showed me that his phone was informing him that the stable version of CM for the Galaxy S4 was ready. He started the download while we ate. Later, when we arrived home, the download was complete, so he pressed the button for the upgrade to complete. When it was done, the phone started to reboot, and stalled at "Samsung Galaxy S4". It never even got to the cartoon android.
The phone was bricked.
"No problem!" I said, cheerfully naively.