As of version 4.0, Farm Works has saved data at a predefined interval (the default is 5 minutes) for as long as it is open. This is designed to preserve your work in case of a power outage, but we are of the opinion that having a box pop up every 5 minutes asking you to save your work. The save interval can be changed by modifying an option in an .ini file.
If you are afraid you are about to mess something up, or you are about to be doing a lot of drawing, make a backup of your project to the C drive. This is just as effective as saving your file when you think about it. An undo option is not very likely in the near future, but we would also like to implement one.