Service layer and UI interface

Question

Generally speaking a service layer is completely separate from UI interface..

However, i would just like to know is there any possibility of some dependency (however little) between UI and service layer? Please give any example.

I am asking this question as we are going to design an iPad optimized UI and we have an existing desktop UI...Now ideally there should be only presentation level or JSP, CSS changes For iPad UI..But the screens are not necessarily going to be 1-1 for iPad..i.e. There might be slight differences (other than just UI design) with the exising desktop version..

So i am asking this question in this context.