True -- however, two points: 1) we probably won't stay with the 'mbox' format forever, and 2) we would like to use the Sieve plugin, which I believe requires use of Dovecot LDA.
Please set up a system using that plugin and make sure it does everything you need it to. I had multiple problems with specific features not being available, plus no timsieved, which then begs the problem of - how will your users manage sieve instructions. I finally mangled a squirrelmail plugin to use local disk for storage instead of talking to timseived and ripped out all the incompatible bits - it wasn't pretty.
I don't want to discourage you :-) but before you get too far committed, make sure that your needs are met.
We also have a very large production environment. Thanks for the ideas.
Good luck :-).
