Update: a few hours later and the phone kept trying to update until it died. I plugged it back in and it went right back to updating. It seems like my phone is ruined since it won't do anything except keep rebooting into the update which never finishes.
It didn't work. Because of where in the boot process the update takes control, the Nokia app never sees that a phone was plugged in.
So, here's what I did. I bought another one. It's 1/2 the price it was when I bought it last year, and it's the best $70 phone out there. I didn't see anyone else have this problem, so I view it as a fluke.
Spent a good 5 hours last night trying to get rid of the duplicate pics and songs that appeared after updating the 521 to Black. I give up...tried formatting the SD card in the phone, on a computer and it made no difference. I guess I will have to do a hard reset.