One form of backup I use on documents is mailing the document from one account to the other.
This works for most documents, but gmail does have a 25 MB limit on file size. When you are scanning documents at large resolutions, I've found it's not too difficult to go over 25 MB.
Google has announced that Google Documents will soon allow you 1 GB of additional storage space for files. (These files won't be converted into Google Doc, Spreadsheet, or Presentation format -- it's simply storage space.) And if you need more space, additional GB will be fairly inexpensive.
The file size limitation will be 250 MB.
We're happy to announce that over the next few weeks we will be rolling out the ability to upload, store and organize any type of file in Google Docs. With this change, you'll be able to upload and access your files from any computer -- all you need is an Internet connection.
Instead of emailing files to yourself, which is particularly difficult with large files, you can upload to Google Docs any file up to 250 MB. You'll have 1 GB of free storage for files you don't convert into one of the Google Docs formats (i.e. Google documents, spreadsheets, and presentations), and if you need more space, you can buy additional storage for $0.25 per GB per year. This makes it easy to backup more of your key files online, from large graphics and raw photos to unedited home videos taken on your smartphone. You might even be able to replace the USB drive you reserved for those files that are too big to send over email.