This is a rather old tip but I am surprised a lot of folks don’t already know this. A couple of (or more) enterprising folks have built an interface that integrates with Windows Explorer and Gmail. The end result being a drive that shows up on the user’s explorer window that users can drag and drop files into, and which ultimately mails these files to the user’s gmail account. My understanding of this utility is that it is pretty safe, but hey, don’t take my word for it. I love using it to backup my MBA essays. I used to use FTP sites, but find this so much more convenient. You can download it from here.
You can set up a filter in gmail to put these mails into a “backup” label. I am sure you can figure that part out on your own.