I have had some problems with the pics, but non have worn out.
I have had problems with them getting ZAPPED!  My R&D desk is
not designed to be that, and I am on carpet!  I have killed 3
chips in the last 3 months.  Well anyway, just thought I would
mention that, in case your problem is not UV at all..  Oh yea
I have not noticed a time increase in erasing chips, but have
notice a big difference between different chips, and different
models.
           Giles L. Honeycutt