It appears to be a stupid idea to backup changes of your project/files on a thumb drive in a era of "Super fast internet, and Cloud computing".
But a friend pointed me out that there are still places in the world where people still do not have good network facilities. Cloud computing to sync data in such a place is therefore out of question.
Although it appears to be a bad idea to write an application that compares difference between a source dir and a usb thumb drive, it can still act as a tool that demonstrates a possiblility and may be in the future it can be extended to add functionalities similar to git or so to say a tracking system between the two directories and copy files using map reduce.
Just specify the source path and usb label, and whenever the same labeled USB thumb drive is inserted, User is given option to copy files that were either modified or is new to usb thumb drive.
Open to suggestions !!! :)