I've been doing some tests of file synchronization with Unison (think "two way rsync"), and run into one problem: Synching between servers has conflicts on the index file. I can manually exclude, but what seems to me to be a really wonderful feature would be to, preferably, make the indexes somewhat atomic, so that files, once written, don't change (this is a feature of maildirs in general), and barring that, that they include the machine name as part of the filename, so there's no conflicts.
Also, on a completely unrelated and somewhat offtopic note: I'd love to hear some brainstorms on how to prevent duplicate messages when maildirs are synched, files are moved from new on one or more ends, flags are changed inconsistently, and synched back.
Ari