Hi,
Thanks for the PM. Sorry not to have responded sooner … bit busy here. Also, I’m responding here so that anyone else can follow this thread and see what I have to say.
I’m not sure why Jaysen thinks I’m the guru in this, but I have been collaborating with a friend in China over a couple of projects now. I’m on a Mac, she’s on Windows — until she can afford to move onto a Mac! — and as we’re working with Chinese, that constitutes a real, deep–down technical problem with character encoding. The only way round it has been for me to install Windows Scrivener on my MBA using Crossover — a non-techie’s, graphical front end for WINE — and cope with whatever loss of functionalities results from that.
We keep our active scriv folder in a shared Cubby — I put her onto that, though Dropbox would do just as well … more on Cubby in a minute. Scrivener puts a user-lock file in the project package when it’s being worked on or is open on one computer, so it can’t be simultaneously opened on a second; if you try to open it on a second, an alert comes up telling you that. On the one occasion when I wanted to work on it and she was doing so, I merely exited and waited, rather than forking the project — Scrivener offers you the choice to open a copy, but that way madness lies as the two versions would be different.
The only time there was a small issue with the project, there was a conflicted document which she dealt with without problem … it was in the early stages of our collaboration through Scrivener, and I think she must have shut her computer down a mite too quickly before Cubby had completely synchronised.
As Jaysen says, backing up, especially to an external drive, is a no-brainer in any case — a friend staying with us had a wine+computer moment a couple of weeks ago; he was lying down watching a movie on his 15” MBP and fell asleep … trouble was he had a full glass of red wine balanced on his ample stomach! Straight onto the MBP. Even more stupidly, rather than getting hold of me immediately, as it didn’t respond, he plugged it into the mains and tried to restart it. End of MBP and he lost all his data as he had no back-up!
The other thing I do, though Shirley my collaborator hasn’t got into the groove yet on this, is take a snapshot when I finish editing each individual document in the project, and if I stop work half way through. I think you should institute that as a sine qua non of collaboration.
Why Cubby? Well, having heard about it from Nom, I gave it a try. Just as stable and secure as Dropbox, gives you 5GB of free space rather than 2GB, but, most importantly, I think, doesn’t reserve a whole folder on your hard drive in which everything to be sync’d through the cloud must be put, but rather allows you to designate individual folders as Cubbies, even folders on external drives, and they will be sync’d.
And, I think even more useful in collaboration, I have Cubby and Scrivener set to give me alerts through Growl, so that every time the project is modified on Cubby, Growl puts up a notification for a couple of seconds. I find it very companionable if I’m doing something else on my computer and Growl tells me every few minutes that she’s working on our project — when I was in China, we used to go to coffee-shops together and sit opposite each other, working on whatever each of us had to hand at that moment 
— and more important, Growl tells me when she closes the project, as I get a message “user.lock deleted”, and I know I can take over. If I am not using my computer when she’s working and finishes, so I don’t get that message, I check my Trash, as the user.lock file will be in there — I keep my Trash empty as much as possible.
I don’t know if Dropbox will send you alerts through Growl in the same way, as I haven’t used it as a Scrivener collaboration space; it may do. But receiving alerts telling you what is happening with the project in terms of your collaborator’s being active or not is extremely useful.
So, I have no qualms working collaboratively that way. If either of us is in any doubt, we get in touch through WeChat — WhatsApp or Skype or equivalent would do as well — and confirm. If you you are both on Macs, you shouldn’t really have any trouble. If your collaborator is on Windows, and you’re not using CJK or possibly other non-Roman languages, you should be OK, though you might run into odd problems with less common accented characters, “guillemets” and such-like … it’s the same underlying character-encoding problem, but you shouldn’t have your whole text turned into gibberish.
Obviously, unless like Shirley and me you have a 7–8 hours time difference, you would need to come to a basic agreement on who gets to work on it when, but I personally think working with the active project in the cloud-space would be more straightforward than using back-ups, as it then becomes unclear what is the “master project”, as your collaborator won’t be working on the file you have on your hard disk but a separate version.
Anyway, best of luck with your collaboration.
Somerset, eh? Briar Kit Esme is in Dorset, I believe; I’m in Devon as much as I can; Keith’s in Cornwall as are several other Scrivenisto/as … West Country rules! 
Mr X
