We do this also with over 150 sites.  Normal file restores are not a problem
but if the box fails or corrupts itself then we rebuild a box here and let
them run over the WAN until we can ship it out over the weekend.  For boxes
coming in over the wan I have a client option set that makes sure they use
compression since some of our links are very slow (56K) Its all been working
well here for years.

The only warning I would give is if you are using any type of connect agent
you may want to make sure you are using a fast enough link.  The exchange
agent especially is not very forgiving of "bumps" in the network.  I believe
this is a safety mechanism built into the agent that protects the integrity
of the stores.  When we first started using Exchange some backups would take
over 36 hours.  Any "bump" in the network would cause the whole thing to
fail and we would have to start all over again.  Now all sites that warrant
their own Exchange Server automatically get their own TSM server.

Jack