It'd be easy when editing the tag for the server to say "Does this name match this user in the imported contact list? Yes? Ok, it's most likely that person then."
I have a lot of noise in my contacts list though. Very rarely do I have a surname, mostly it's suffixed with "home", "mbl" or "work" or even city name as surname sometimes. I'm sure a "best guess" would be possible, I'm not sure of anyone that religiously stores first/last name aside from pure business contacts.
With smart phones with keyboards and cloud sync I think more people are starting to. I do now, and have since 2008 when I started using a smart phone. I've noticed more people switch over from short nicknames to full names with easier input. It's easier than going to your contact and saying "who the heck is James?" Now I just keep as much data as possible on each person. That way I also have their address handy, in case I need to mail them something. I've been meaning to start keeping birthdays in there too, so I can get a notification on my phone.
