I use it exactly as a master for my PSDs for a year or so and I've been really happy with it, even when the file is open on another machine or two while I'm edi

I use it exactly as a master for my PSDs for a year or so and I've been really happy with it, even when the file is open on another machine or two while I'm editing it on a a third. If there's a potential to flatten the file upon save, I'd create a second directory for those files and keep them separate from the PSDs. If you really don't trust accidents not to happen, maybe create read-only or password-protected masters in addition to those editable PSDs. They've also got the backup/versioning service you can pay for.