Realeyz:
What I believe Wlonh is refering to is the fact that the clearance between the keyboard and the screen when the iBook is closed is very thin... in the Pismo PB series a problem arose that when closed the keyboard actually touched the screen, causing marks to be left. Any such product as you mention would in effect close the gap between the keyboard and the screen, perhaps causing a similar situation. Hope this helps.
Cheers!
Chris