My experience wasn't too pleasant and not sure how frequent it is with others (haven't read this whole thread).
Anyway, there was an error during the update process on my iPhone 6. I powered the iPhone back on and it had a screen showing to plug it into the PC for iTunes. It was already plugged in, so I just unplugged and restarted iTunes, replugged in phone, and then iTunes told me I had to restore the iPhone.
So, I went through that process and it gave an error again. I was back at that connect my iPhone to iTunes screen again. Tried the restore a second time and same deal. Said okay forget this, went to Apple Store and they did a factory reset there to 8.0.2. Back at home I restored all my stuff from a backup that was done before the original attempt to update and everything seems back to normal now. I haven't experienced any issues thus far other than the update effectively bricking my iPhone.
I'm not sure what would have caused the error to begin with since nothing extraordinary happened on my side while it was doing the update.