i've heard some ppl do it every 3 months...but this is the first time i've ever used it on my TT, and its outstanding...i have always loved the NXT...i think its wonderful...i just applied the zaino, so i cant really give my opinion on that yet (but i was freeloading the zaino from Ali =) so the price was just fine for me)
look at pat's post a couple lines up...he prob knows more about these products than anybody...you should ask him...he also sent me some great links a while back on cleaning the car and how to do it properly...and i'm obviously sticking with those guidelines every time i clean the car...thanks pat