It's easy not to realise data is stored inside of a particular program, rather than more easily backed up Documents folders etc. When I was very young (13-ish, year 2000) I lost primary school photos because I didn't realise that they were stored inside the Program Files directory of the Kodak camrea download software I was using and not inside of the Documents and Settings directory.

Ever since then I now backup and image the entire HDD and I have almost literally terrabytes of extra OS images "just in case" I forgot or lost something. Hasn't really happened yet. Except I still can't find my Bitcoin from 2010. Doh.