Where you can get caught out though is if you open up an old project to say try a different effect, different layout etc, even when you close the project and choose "Do not save changes" PD has already saved the changes and you loose your original saved project.
I forgot to turn this off when I re-installed PD and just lost 9 minutes of a 10 minute saved project. I decided to try a different format to render my project so I cut out all but a minute of the project just to save time in rendering.
As I was closing down the program I thought, bugger, and then realised that my project now only consisted of the 1 minute I had just rendered. So be careful people I got off easy I would not like the same to happen to me with an hour long project that I had just spent a week editing.
Cheers
Robert My youtube channel====> http://www.youtube.com/user/relate2?feature=mhsn