yeah that is becomming a common problem with the iceBooks. One guy told me that he turned his 'book off and just opened and close the lid for like 10 minutes and it eventually went away.
I don't know about you, but that just doesn't seem normal. So I got a WD-40 can (with the straw) and just sprayed a little on the edges of the hinge and that cleared it up right away.