We use Dropbox to transfer the prepared OpenLP service files from the church office PC to the in-church projection PC, but what I've found is that both PCs must have the root DropBox folder in the same absolute path, not under a user account. This is because OpenLP stores the full/absolute path for media, images, presentations, themes, etc. in its databases. Whilst all the objects for a service are encapsulated into the resulting osz file (i.e. a .zip file named .osz), the rest of the loaded objects need to be in the same path as stored in the database otherwise they're not usable.
Also, whilst I haven't tried it, I presume the Mac version uses Mac syntax paths for media etc. objects in the databases, so would be incompatible with a Windows version, making Dropbox sync not possible.
Basically, a way needs to be found to make all stored object paths relative to the OpenLP/Data folder (& optionally copying them in there if not already), not absolute, and in a common, version/platform independent format, such that service preparation may be performed on a Mac, sync'd via DropBox (or Drive, etc.) and then projected from a PC, whilst retaining full setup capability by the projecting PC.