NOTE: This article has been superceded by an updated one here!
BitTorrent Sync is a really useful alternative to Dropbox / Google Drive / etc, as none of the files are stored on someone else's server and you can have as much space as you want!
BTSync can only be run once (per user), so running it as a service ensures it starts at boot for every user without them needing to log on!
Attached are two files, the first is an init.d script that allows you to start / stop / restart the BTSync service for each user - this needs to be moved to /etc/init.d/btsync - the second is an example configuration file for BTSync, to be moved to ~/.BTSync/config.json
When this is set up, simply run
update-rc.d btsync defaults
to install the btsync service, or
service btsync start
service btsync stop
service btsync restart
to control it.