Online backup makes some people nervous. It shouldn't--especially with program-and-service combos like MozyHome (2GB storage free, other plans available) around. With 128-bit or 448-bit Blowfish encryption, there's no way anyone's going to steal your data. Mozy actually goes out of its way to warn you that if you forget your password (Mozy can also provide one which they keep track of), there's no way to access your data.
Mozy is a product of Decho, which is owned by industry giant EMC. In other words, the data you send to them is safe--a lot safer than that data you back up locally. A 2GB account is free, which may raise an alarm for some, but it's actually a leader to the US$5 a month unlimited plan. Most people can back up their essential (tax data, love letters, wedding photos, etc.) with 2GB, but many people (myself included) can use a lot more.
MozyHome provides a somewhat homely client that sits in the system tray backing up your important data in the background. You can let the program automatically search for said data, or define it yourself--explicitly or by the use of filters (e.g., *.xlsx). The only other settings that matter control how aggressive the program is about backing up, i.e. how long the PC should be idle before backup commences or the CPU usage threshold over which backups won't occur. E.g., CPU usage = 30% by other programs, no backup occurs. You may also simply have the program back up at a specific time and leave you PC alone the rest of the time.
The initial backup can take quite a while, depending on the amount of data and the speed of your upstream connection. Subsequent backups only upload changes and are far quicker. Previous versions tended to bog down the computer at times--especially when dealing with large data sets--but this latest client seems better-behaved. If you're already a user, make sure you update the program if you experienced these issues. Restoring files is simple: Click on the Mozy virtual drive that the program places in Explorer and drag back the files you want.
I've actually been using Mozy for several years with great success. I recommend it highly and often. Fabrik Ultimate Backup is a similar product that offers comparable deals and software; that one's worth a look, too.