[Toadling]

From my observations, it seems the database file (actually a bundle of multiple zipped XML files) grows as you conduct transactions (i.e. add/edit/delete items). I think OmniFocus has been using this, or a similar model, for some time now.

Those zipped transaction files seem to hang around in the package until you sync to your remote server from your Mac, then sync your iPhone (or another Mac, I suppose), and then sync the original Mac again. I suspect OmniFocus does things this way to help ensure data integrity. Consequently, it's probably best to let it sync frequently so you don't get too many transactions piled up waiting to be processed. Of course, this is all speculation on my part.

In the OmniFocus for iPhone FAQ, it's recommended to keep your total number of actions under about 1,000 items for best performance. It's not clear to me, though, if this includes items that are "on hold". In other words, can I put things on hold to reduce my number of synced items to around 1,000? Also, what's the best way to find out how many items I'm syncing? Do I have to count them manually?

-Dennis