Jeff,
We are currently using a TL812 DLT 7000 Tape library.  It contains 48 slots
and 4 tape drives.  We had many problems with tape I/O errors until we
upgraded to a firmware level above V70.  We are currently at V100 and the
product seems to work pretty well.  It takes about 5 minutes for the
library to load a tape and down load data once a customer requests a
restore that is off-line.  The DLT tapes are around 20GB each(using only
hardware compression-on ADSM, compression is turned off).  Unfortunately,
 we are running out of space, and soon we will require another storage
library.  Our server is an RS/6000 F50 running AIX 4.2.
Restores often conflict with our admin. schedules(migration, space
reclamation).  Restores have priority with all admin. schedules except
migrations. It just takes longer with a conflict.   -  I always have at
least one drive available for restores- availability  will become more of
an issue with us as clients are added-  that is why we are looking for
another tape library.  I couldn't tell you exactly how many restores are
done daily.  I get called when someone feels they are waiting to long for a
restore(couple times a week).
If you don't want to check in /check out tapes all the time, get a large
tape library and tighten the number of revisions you have on your
policy/management classes.     I hope that helps you.

        Andy Schauerte
        Honeywell Defense Avionics Systems
        (505) 828-5383