been running with six 3494's for 5+ years...
Love'em !
had them spread out across 4 data centers in 3 states...
as environments have changed I've been able to pull resources (cabinets &
drives) from one ATL and put them on another
very flexible
the six I deal with were bought new 5+ years ago and I've had very little
problems
two accessors suffered a resistor burnout that required a board replacement
        each time the library was just put in manual mode while IBM went to
get the part & replace (net results of zero outage)
we do have an excellent IBM CE as far as PM goes !
we run dual grippers (which is a flip of a coin)
right now our configurations are
        1-2frame 6-3590
        2-3frame 6-3590 (ea.)
        1-6frame 12-3590
        2-8frame 16-3590 (ea.)
I think I got that right... well, they will be that way when my most recent
movement of frames is complete ;-)
Oh, and they (all the tsm environments) take in 1.5-ish TB of compressed
client data nightly so there are a lot of tapes being written & reclaimed
daily
Dwight