I have heard the same thing from many guys we have installed NOS for over the years. At first they love it because its a lot of power for the cost and it helps them smack down a few other guys they have been trying to beat. But the newness wears off pretty quick and then they dont use it all that much if at all. Filling the bottle, heating the bottle, bottle not open when you want to race, something not working in the system, etc. these are all things that become a pain in the butt to the casual NOS user.
The guys who use NOS and keep it are the racers. They know when they are going to use it and are prepared to use it. It helps them attain the ET/speed that they want and its great and pretty reliable too. But the casual guy who might use it every now and then gets tired of it.
Heads/cam, SC, turbo, stroker - the power is there all the time. When the fast bike pulls up next to you and looks over and wants some you wont be able to ask him to wait a few minutes while you heat your bottle up to get decent bottle pressure.
From the numbers I am seeing a lot of guys get out of the Paxton, it seems to offer a pretty good bang for the buck and its there all the time.
Good luck with it!