Thanks for all the great advice. I definitely have had sagging shelves
in the past -they were fixed to the case and could not be flipped over
to invert the strain vectors. A staff at a bookcase store I visited
yesterday recommended shuffling the books around from shelf to shelf
once a month as a general practice.

> I have some particle board shelf that seem to be able to stand up to

the

> weight....I got them about 5 years ago from Staples - the shelves are ~
> 1.5 inches thick and 3 feet long, cantilevered on two small pins on
> either end.
>
> I think the sagging issue would be related to shelf thickness, length,
> and the support mechanism for hanging them. Thinner shelves could work
> if the method for supporting them is different.