[sigil]

Well, dropbox could just listen for fs events inside the DropBox folder...

On Linux at least [1], this is exactly what the Dropbox client does. It only registers inotify watchers on the $HOME/Dropbox directory and subdirectories. To verify:

    strace -f -e trace=inotify_add_watch dropboxd

You could also strace open/stat/read/write syscalls to verify that, aside from shared libraries and the like, the Dropbox Linux client doesn't access files outside of your Dropbox directory.

Other OSes have different file monitoring capabilities though. Anyone up on file monitoring on Windows / OS X? Is directory-specific monitoring possible?

[1] https://www.dropbox.com/install?os=lnx

[radiospiel]

> Other OSes have different file monitoring capabilities though. Anyone up on file monitoring on Windows / OS X? Is directory-specific monitoring possible?

yes

[MrDosu]

But ReadDirectoryChangesW notoriously misses updates. Also it would scale horribly to large amounts of files.

NTFS has a feature called Change Journals where you can view a volume as a stream of changes.

[0942v8653]

OS X definitely does, it's quite simple and reliable.