Do you wear glasses? Do you have a peakvisor on your helmet? Sometimes the need to tilt the head back further to see under rims or the visor can be a cause of neck pain.

You also don't indicate what sort of pain and where. Is it around the vertebrae or the musclar part of the nape?

Have you been back to your chiro? That might be a good reference point, especially if you can replicate the position your neck and head is in on the bike.

Otherwise, Shermer's neck is a relatively common complaint among long-distance cyclists, although it manifests itself more in the 600+ randonnees.

Here's a reference for you:

www.ultracycling.com/training/neck_pain.html

that Machka has just given me. It's entitled: "A Pain in the Neck".