I’m not sure what kind of syncing problems you’re having, Simon, and I’m sure it’s been hell, but I’m not seeing too much of a problem with the idea of syncing Scrivener projects per se. I take it that background syncing over a network with a package format has been established as unreliable, especially if it happens in the background as you work, but that’s the nature of the beast across the board, I would think. But if you’ve got two computers that you shuttle between on a regular basis, this kind of fragility is the least of your worries – what about leaving files open on one machine, and opening them on another, etc.?
I have a different approach to syncing. I use an SD card to shuttle my dissertation files – Scrivener project, bibliographic database, DEVONthink database, everything – between my “desktop” machine (a 17" MacBook Pro) and my “laptop” (a Hackintoshed Dell Mini 9 netbook). That’s right, OLD FASHIONED SNEAKERNET. Because the transfer is physical, there is no ambiguity. No SD in computer, no dissertation work. Simple as that.
On inserting the card into either machine, it fires up ChronoSync and mirrors the contents onto the computer in question, based on a “package dissection” sync method, which only copies changed files within packages, making it quite fast. (It’s possible for this to go wrong if you’ve independently opened files on each computer between syncs, but because I only work on a computer than has the SD card in it, I haven’t had any problems.) This action also triggers a specific, customised “dissertation Dock” (via an app called DockSpaces) that contains Scrivener, DEVONthink and Bookends in it. I do my work. When I want to swap computers, I double-click a little Applescript app that quits all the relevant apps (none of which ask for save confirmation, because they all autosave), syncs everything again, ejects my SD card and enables a customised Dock that doesn’t contain Scrivener, DEVONthink or Bookends. The latter is an addition reminder to me, on top of the ritual attachment to the SD card, that dissertation work is no longer possible. (You could actually let the files live only on the transfer media itself, but that’d be dangerous.)
To present it simply: Insert card. Work. Eject card. Go to other computer. Insert card. Work. Eject card. I haven’t had any problems with this system. (People, please let me know if I’ve overlooked something, or are headed towards disaster!) I’ve tried all sorts of other, fancier systems – each computer syncing to a LAN file server, an online server, or using multiple mobile accounts that mirror to an OS X Server master account, you name it – and there’s always a point at which it’s possible to screw things up, simply because it’s possible to keep files open in different locations, etc. By ritualising it, and tying everything to the physical presence of the transfer medium – something very tangible to my weak mind – I think I’ve overcome this problem.
Until LAN or WAN connectivity gets as good as having a USB or FireWire drive physically attached to your computer, or until operating systems can enable the seamless integration of live changes to single files in multiple locations, I don’t think it’s really possible to access the files of a desktop app from different locations without having to take some sort of regime of care (e.g. making sure apps are closed before syncing, or intentionally copying files to and from DropBox/fileserver/VPN/whatever) or ritual (e.g. my sneakernet workflow).