I currently have a nokia phone from 2005 running verizon backup assistant.
When I get my galaxy nexus, it will immediately import my gmail contacts, correct?
Will I then need to use verizon backup assistant to import my current contacts?
Will they replace my gmail contacts? Will they all automatically be added (creating hordes of repeats)?
Yes - Android phones default to syncing your gmail contacts.
Android also has the option to store contacts locally. I don't know if Verizon Backup Assistant does that, someone else will have to chime in.
If you have locally-stored and gmail contacts in common, you'll get duplicates.
If you can get all of your contacts on Gmail/web, then there's a tool on your Gmail/Contacts web page to weed out duplicates.
I've personally gone thru the local+gmail duplicate thing myself - others may know a better way, but I found it was best to just get all my contacts up to the Gmail web, sort them out there, and leave other tools out of it.
If you can export your Nokia contacts into a Vcard file (vcf) - Gmail/Contacts on the web will allow you to import that file. That's what I did in my case (non-Nokia, non-Verizon) and that worked out well for me.
Having all of your contact backup with Google just works and there's no lock-in -- you can always export out your contacts in a Vcard file also (that's an address-book standard if you're not familiar with that term).
Hope this helps, and hope Verizon owners catching any rough spots here specific to Backup Assistant will chime in as well.