[Andrew]

Single-file sharing is inherently safer if you never have two copies of OmniFocus running at the same time (and our file-locking mechanism should more or less enforce that).

Syncing is generally stable right now, but management of multiple clients is tricky, and the current biggest issue is that it is possible for a configuration to get into a state where older transactions don't get cleaned up properly, causing file bloat and making syncing slower. Of course, the big benefit is "offline" use with multiple clients, which you simply can't have without some sort of syncing solution.