In addition to saving locally within Trainz, I also make a seperate backup of my content to a CDP then copy the CDP file(s) to another hard drive for eventual burning on to a CDR or DVDR for permenant backup.
I think of the local copy as the "scratch" version that is being worked on, and the backup copies as current active versions. Each one of these backups is useable at the stage of the backup so it's easy to go back at any time without missing too much other than my current work and some wasted time.
This method has saved my butt a few times because I was able to backtrack and recover from major changes. If I plan on doing any major updates to my route, I will make an extra CDP file first so I can recover even quicker.
John