Watching the Paris-Nice prologue I saw the Discovery Channel Team warming up on the trainers .?

Question

What was the stuff they had in theirs noses and of what use did it serve?

Answer 1

sometimes a few cyclists will use a decongestant (like Vicks) to help clear their sinus before a race
not sure if that is what you saw

Answer 2

They are called breathe right nasal strips. They were developed to prevent snoring. They hold the nasal passages open. Many athletes use them to aid breathing.

http://www.breatheright.com/products/nasal_strips.asp

(Another best answer for Uncle Neal? even though he hasn't a clue what he is talking about. Oh well it is not the first time)