We have Subversion repository on DWM's home Linux system. This system is up pretty much 24/7 to provide internet connectivity for his household.
Note that you can only connect to this server via SSL, for security reasons. The server has a certificate that was signed using a self-created SpookyDistance root certificate, so you when you try to access it for the first time, you'll be notified of this unusual circumstance. If you don't want to trust receiving the certificate over the net, contact DWM for a hand-delivered copy that you can load into your browser and into Subversion.
The repository was initially loaded with the latest sources (no history) from a CVS service that we had for a while. The SDx software, such as it is, is under /sdx/trunk. Feel free to create your own top-level branches to store personal stuff related to SDx.
The best way to assure that something related to SpookyDistance will be backed up is to check it into the repository or post it on this wiki. See Operations for the backup schedule.