I just got a Samsung Galaxy Nexus.
And I've re-flashed it with the Google Jelly Bean image.
And my wife did it to hers... without a single problem and without my help.
My Oldest daughter flashed it with Google's image from the onboard storage putting the file there using Windows and MTP device transfer. She was the first of us all. I said I was gonna do mine and she wanted to do hers first for some reason.
She convinced my Son-In-Law to do it... he is even less adept than my wife or oldest daughter.
All four of us are running Jelly Bean. I was completely impressed with my wife, daughter and son-in-law. I did it last of the four. Almost shamed into doing it.