I have found them to be excellent. I have been down to their headquarters to sort something out and it was done while I waited. You have to book in advance, I don't think you can just turn up but a phone call is all that is needed. While I was there another photographer came in with a D3 issue which couldn't be sorted that afternoon so they arranged a loan camera.
They have an exclusive dept. for NPS photographers and I went to a product road show last week which was a good day. They keep in touch offer preferential help for supply and support to NPS card holders.
It's easy to join, well it was for me, initially I had an NPU card and they contacted me to say I could upgrade to NPS. You have to have two Pro bodies and two Pro lenses, as I remember. You also have to prove your a working Pro but you obviously are so that shouldn't be a problem. "NPU" is Nikon Professional User which is a lesser program for owners of Pro gear who aren't working Pro's.
I was a CPS user but that was 5 years back and they went through a bad time, moving locations and putting the dept under a different set up. No idea what they are like now but back then they had problems which have hopefully been sorted.
I may sound like a Nikon rep. but I'm not.
David