We're using an STK9714 on ADSM V2 on an RS/6000 R50 running AIX 4.15.  Our
library has 4 DLT7000 and 100 slots.  We chose the DLT7000 for it's speed
and the STK for its expandability (it can hold up to 6 drives).  

The good things about the library are it's speed and capacity.  We were
using a pair of IBM 7331's with 8mm.

The bad things... we went through all the backlevel micro code problems
that everyone else did.  And in addition, we had a mystery problem that
couldn't be nailed down.  The library wasn't dismounting tapes properly. 
The dismount command would be issued, and ADSM would think the tape was
dismounted, but it would actually be left in the drive.  Then later when
the tape was requested again, it's home slot would be checked, and found
empty, then the tape would be marked unavailable.  The library would also
try to load another tape in the drive that the tape had been left in, and
get an error.  The problem was finally traked down to bad cables between
the library & RS6000.

A new problem was just discovered on STK9710's (Anyone who has one should
check this).  The library maintains a counter on how many times the
cleaning tape has been used, after 20 times, the cleaner should be
replaced.  But the counter isn't incrementing.  So you may be "cleaning"
drives with a dirty cleaning tape.

All in all, I'm still gald we went with the STK 9710 & DLT7000 drives, but
it hasn't been easy.  Some problems were DLT related and some were STK
related, but the performance & expandability were worth the headaches.