Rob Lewis wrote on Nov 7^th, 2010 at 12:10am:
The Bookmarkshelf (.bkmslf) file should work OK because, like several other well-made apps out there (BBEdit, for example), BookMacster watches open documents for changes and automatically re-reads the file from the disk.  So if you (or a BookMacster Agent's Worker) saves new changes to the Bookmarkshelf file in /Users/Shared/, on Mac User Account "A", then when you switch to Mac User Account "B", even if BookMacster is running and even if this Bookmarkshelf is open, it will automatically read in the changes.

Things might get a little dicey with Agents running on both accounts, though.  There shouldn't be any database corruption, since even though "A" and "B" are different users, they're accessing via the same filesystem and sqlite file locking should prevent the two Agents' Workers from reading and writing at the same time.  Let's say that you triggered an Agent by, maybe adding a bookmark to Safari on account "A".  In order to throttle unnecessary processing, BookMacster's Workers wait 60 seconds before doing anything.  In the meantime, let's say you fast-user-switch to account "B" and, say, quit Firefox, which triggers another BookMacsterWorker over there.  The Worker on account "A" will continue to run, and the two processes might try to access the .bkmslf file at the same time.  One of these processes would probably fail to complete and display a "SQLite Error: File is locked", or something like that.

Rob Lewis wrote on Nov 7^th, 2010 at 12:10am:
This would eliminate the possibility of local filesystem conflicts described above, but again if things get changed to quickly on multiple accounts, JungleDisk may occasionally indicate conflicts.  That's true with any file-syncing mechanism.

So, the short answer is: Go ahead, but take it easy with Agents.  If you're using Agents, click the Advanced view and select some triggers that are unlikely to conflict.  The Scheduled trigger is always the safest choice, if your life is predictable enough to work with that.

Let us know if you have any trouble.  Just thinking this through, I've realized some things we could do in future versions to make this more reliable.