The following may be a simpler option to consider when you consider that a USB drive can easily get misplaced.
MOZY (MozyHome Free) will incrementally backup user selected file types (text documents, spreadsheets, email, etc.) online. Set it and forget it - it will attempt to run daily backups (user configurable). You can get the first 2 GB as 100% free backup space:
http://mozy.com/home
It can upload up to 100MB per hour so the initial run can take some time. Therafter, it often only takes minutes to incrementally backup any changed or new content.
If you ever lose most of your data items, it will likely be necessary to have them burn you a DVD (for a fee) since your most basic alternative is requesting limited selected files retrievable from email (normally a 10MB account limit, here) as a ZIP attachment.