I received my 600 yesterday, and the included sleeve is not enough to protect it. It's too thin in my opinion.
In my order I included the
Sony standard cover for the 600 which does the job fine. It fits in the holes on top and bottom of the reader and is sturdy. It's a flip-over casing with a leatherlook on the outside (not sure whether it is real leather, smells that way though) and a soft fabric on the inside.
It cost me 29,95 euro's I believe.