To the observed problems reported by other 3494/3590 customers I would
add:
 - Rack problems: The cell racks used to store cartridges on
   the walls of the 3494 are large plastic assemblies supported only
   at the edges, and when filled with heavy tapes they noticeably sag
   in a catenary manner, making the matrix irregular and resulting in
   cartridge storage problems, such as tapes ending up sticking out of
   the cells after being stored (which of course can damage the robot
   and tape as the robot goes speeding by).  The robot can partially
   compensate for this misalignment by doing a little step downward
   before accessing the cell (which you can observe by watching
   carefully).  In concert with central hardware support, our CE had
   to put a piece of black tape over part of a fiducial to help
   overall alignment in one case.
 - Inadequate PC: IBM habitually deploys underpowered PCs as embedded
   systems in hardware like the 3494.  In the case of the 3494, this
   OS/2 system is so slow that it takes a very painful 20 minutes to
   reboot the box.  Its inventory process is so slow that most large
   shops have disabled reinventorying, and do it only if they
   absolutely have to, as it renders the 3494 unvailable in the mean
   time.  Response time is sluggish for console and network queries.
   The 3494 is being sold as an "enterprise" system, but is not
   provided with a controller which would allow it to live up to that
   level of performance.
In general, the 3494 is an excellent product, but suffers from some
engineering problems which make customers and hardware support
personnel shake their heads.
The 3590 tape drives are outstanding technology which have been highly
reliable.  We encountered a couple of failed power supplies, and once
a tape snapped.  But those are rarities amidst excellent performance.
        Richard Sims, Boston University OIT