leave it until it gives you an error message, or a complete message. dont unplug it or cancel the update.
Too late
It was just on the backup process, and threw me a few errors - I did a battery pull, and going to attempt again.
This time I deleted Pandora off the phone.
As mentioned in the .160 thread, 4.5.0.160 does not work well on Verizon. There is a problem involving a chirp/squeal sound while in a call, which is very annoying. One other member reported it happens on Cellular South as well.
You can upgrade to one of the hybrid OS builds though and have most of the .160 files, but use the radio files form .131 which fixes the issues with .160: