100 GB per server - not us. 100 GB over 3 servers - Yes.

Exchange can certainly cope with servers that large, but you need to
consider carefully your restore speed. Restoring a database of this size
will take a minimum of 4 hours - and quite probably longer. Before you can
restore the data base you have to re-build the system, NT and Exchange.
After the restore you need to check the system carefully. That would be (a
conservative estimate) 8 hours down time.
Exchange doesn't go down very often, but when it does it becomes critical
fairly quickly.
It is not just the database restore time. Also the log files that need to be
replayed after a system crash and re-start, or the database analysis tools,
take time (measured in hours, not minutes) to run.

We decided on smaller servers just because of this restore time problem.
Real life? Out of the 35 servers only one has needed restoring after 12
months of use.

Whether you use ADSM or a different backup mechanism does not make much
difference.

Cheers, Chris