Lots of good comments here -- just a few comments to amplify on some things:
1. My CCC utilized the theory that doing the Neck Dissection first, before radiation and chemo, had the advantages of a)cutting off the metastatic highway immediately; and b)making the surgery itself easier, as radiated tissue is not involved. One doctor explained that since they don't know with certainty how the tumors will respond to the radiation, allowing nodal metastasis to remain in place increases risk of further spread before the radiation can have effect. (Of course, much is dependent on tumor location, etc.)
2. I had both submandibular glands removed in my ND (both negative for SCC). I get along pretty well, but then again, don't know how I would be doing if I had them.
3. Most of the literature indicates that avoiding Level V significantly reduces the incidence of shoulder problems, as the SAN and brachial plexus are less likely to be compromised. I had Level 5 removed on both sides. The price is pretty persistent shoulder pain, some weakness in lifting or holding thigns for extended periods of time.
I can still hit a 5 iron 190 yards, though, so all is good. ;-)