Tivoli Continuous Data Protection for Files
Playing on the big stage where literally billions of dollars of data is at stake also tends to weed out weaklings--CDP has been around for a while. It does exactly what you need done, does it reliably, and stops there. It watches folders and files you specify and copies them to both a local storage destination and an external destination such as a network drive, keeping as many revisions as you want. You can use encryption and compression or stick with plain file copying.
Once configured, CDP for Files sits in the system tray and does its duties with a minimum of fuss. I noticed no system slowdown, but there's a right-click option to disable the program temporarily if you're doing something disk intensive. IBM's CDP for Files is a bit pricey, but it works well, and there's just something about having software with an enterprise bloodline protect your data that gives you peace of mind.
--Jon L. Jacobi