I am at the whim of my clients. I can recommend, request as well as try to cajole but at the end of the day I am often not allowed to install software and certainly not allowed to create data repositories. The good news is that the vast majority of clients have used some form of version control for a long time now. I have often disliked the systems or practices employed but they are always better than nothing (and lets face it sometimes dislike doesn't mean they are wrong ;-))

Worst case scenario, I use a similar file scheme to Steve's (probably like most other people).