Lifehacker's top 10 uses for a USB Thumb Drive lists data synchronization as one of the tips. One of the comments within the data sync article recommends Windows SyncToy (a free download). It's been invaluable for me. I use SyncToy to

• Backup my entire MyDocuments folder to a secondary internal hard drive about once a week.
• Backup my Thunderbird mail folder containing emails going back several years to the secondary hard drive about once a week.
• With file sharing enabled on my local home network, sync my teaching and departmental administrative files to my laptop before heading to campus and back again when arriving home.

The first time you use it to create a backup, it can take a while to copy all files to a new location (depending on the speed of your hard drives or network). But otherwise it is relatively fast. My MyDocuments contains almost 40,000 files, and it only takes a few minutes to do the backup. It also provides a variety of backup options for how the backup should occur--synchronize, echo, subscribe, contribute, and combine--such as whether or not you want changes to your secondary installation of files to overwrite changes to your primary file folder location.

SyncToy is available for both Windows XP and Vista. This has been such a useful application, I'm really surprised that MS did not make it a feature in Vista.