I finally went through with this the other day. Got DNS/AD setup, seized FSMO roles on the 2012 server, migrated DHCP etc. I thought I was ready to go so I turned off the 2008 server yesterday. Everything worked fine for a few hrs, then network drives started breaking and a couple of apps broke that must somehow be pointed to the 2008 server for DNS. I initially ignored a WINS migration because I thought that was more or less a legacy service for older versions of Windows. I'm kind of scratching my head on this, any help is appreciated.
edit I've since turned the old DC on to keep things from breaking.