I had a pda film screen protector on my new ipod while I was waiting for my case to arrive. Upon removing the film, there was some residue that I tried to remove using a small amount of WD40. Though I was careful not to get any in the gap around the click wheel, a tiny bit seeped in and now the scrolling function of the click wheel doesn't work. Luckily, I should be able to return it.

So, WD40 and similar products are a no no. Also, adhesive film protectors (at least the ones sold for pdas) are designed for glass. On lucite, they leave a residue that is almost impossible to remove without scratching.