I'm absolutely in love with this stuff. I use it pretty much every day and it does wonderful things to my hair. I don't mind forking over the money for it, because it just does such wonderful things to my dry-ish hair. I avoid the blow dryer, but I still definitely feel the effect. Unless I accidentally use too much, my hair never feels greasy or heavy and the scent is just heavenly. I've also recently started using their shine spray. I fidn that you have to be very careful with this, because, even more than with the oil, a little goes very far. It does give an incredible shine to hair and, unlike other shine products I've tried, the shine stays throughout the day. I've never noticed any problems with dull build up on my hair from the oil, so maybe I've been lucky.
As far as a long term effect, there isn't one, but a long term effect on hair is pretty much impossible. Hair is dead and although you can apply products to make it look and feel better, it doesn't have any way of absorbing ingredients that would allow new growth to become healthier.