I'd have to say we are happy also.  We have over 18 exchange servers with 10
to 30 gig dbs.  All 18 incremental finish well within 2 hours each day.
Full backups take 1 to 4 hours each depending on the load on our AIX ADSM
server.  All Exchange backups are done over gigabit Ethernet.  One drawback
is Microsoft's lack of an API that allows message extraction from the
backups.  We have a mixed Notes/Exchange mail environment.  The Notes users
still enjoy the ability to restore deleted messages long after they were
"accidentally" removed.  Exchange users have a 15 day deleted item retention
period they have to go by.