I'm not sure what benefits people were expecting, but if they thought a ceramic coating all alone would make a drastic difference in the amount of heat they feel on their foot and leg, I'm sure they were disappointed. While some places might hype their product with such claims, and might even be able to provide temperature readings that show a difference, I don't think too many riders have calibrated legs that can easily tell the difference between 1000°F and 900°F for instance. F'n hot is still f'n hot.
I would expect an internal ceramic coating to help keep more heat in the pipe and increase exhaust velocity, but without strictly controlled testing I wouldn't claim any particular amount of difference. As for the external coating promoted by several companies, I feel like those are probably beneficial in terms of the long term appearance of the pipe but once again I've not seen scientific evidence of any heat reduction or performance improvements that are also implied by some of the companies. If I had a set of pipes with cosmetic issues that were otherwise in excellent physical condition, I'd be inclined to use one of the Jet Hot type coatings in the color of my choice to renew the appearance. But I wouldn't do it just for a supposed performance improvement that would be hard to prove or feel.
Jerry