Lost a Yubikey in the last few days. Even though I use 1Password to keep track of where each of my 2FA devices is registered, it's quite a hassle to go through each site, remove the old device and add the new one. It'd be even more tedious if I didn't keep meticulous notes.
It's a pleasant reminder of just how many services support U2F for 2FA. But it really brings home that this system isn't going to scale up to hundreds of logins per person without a bunch more work on the logistics.