For this reason, you should probably invest in a , such as the supertough ($350 for 1TB), which is both waterproof and fireproof, or the versatile, hot-swappable ($369 for 2TB). You don't have to every 5 seconds, but it is a good idea to back up the machine whenever you can remember to do so. It's also wise to keep sensitive documents off portable machines and drives entirely, if at all possible.

For backing up recent documents, I prefer using such as Dropbox or Mozy. Cloud-based backup services are much more convenient because you can access them from anywhere you have an Internet connection, and you don't have to plug your laptop into a physical hard drive.

gives you 2GB of free storage space, which isn't enough for an entire hard-drive backup, but is usually plenty of room for recent documents and files. Dropbox works by putting a folder on your system: All you have to do is save a file in that folder, and it automatically syncs with Dropbox's server. The benefit of this autosync process is that even if someone steals your computer right then, you'll still be able to access that file by signing in to Dropbox from another computer.

is more of a traditional backup service. For $6 a month, Mozy gives you 50GB of space for your entire hard drive (if you so choose). Mozy also offers multiple restore options, including Web-restore and DVD-restore, as well as through the Mozy software client. Restoring files from the Mozy cloud is a more involved process than simple syncing, though--it's backup software, not file-sharing software.

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