I just got back from my local Sony Store - they had a few PRS-350 left (no 650) and I bought the cover for the PRS-350.
It is very nicely made, and this time around, compared to the one for the PRS-300, it was built so the front cover easily bends back without making the back cover slip to the right, which eventually almost cut the side of my right index finger (okay, slightly exaggerating, but it wasn't comfortable). The cover always stays almost flush with the reader!
I think Sony does still listen to their customers