I got this reply from someone that was analyzing several sync programs -- What do you think??
I would suggest looking at either Yadis! Backup http://www.codessentials.com/products/yadisbackup.html
or AutoVer http://beanland.net.au/autover/
Both of them will monitor a folder or a file for changes, and make a backup as soon as any changes are detected. They can also creat versions of the files so that you can go back to older versions of a file.