I don’t use online backups, but they can be convenient. Be sure you have broadband, because you will be uploading lots of data, and it can take hours to do the first backup, even over broadband, and lots of time if you backup large files, such as photos and music.
Some online backup services are free, some aren’t. Some advertise that their backups systems are in this country and have US trained phone support. It’s best to read about a number of them before you choose You also might consider security: if you backups are encrypted so no one can see the contents of your files (eve the backup service).
Once you start using an online backup and the first full backup is done, most systems will only backup your files that have changed since the last backup. This saves lots of time over simply copying over all the files again and again.
Apple has their own backup system called MobileMe, and in addition to backing up your files, you can synch your bookmarks and address book entries among many different Macs. It’s $99 a year.
Mozy is popular and they offer a 2 GB free backup account for Macs.
iDrive also offers a 2 GB free backup account.
Jungledisk is 15 cents per GB with no limit and all your files are encrypted.
Search and you’ll find many more. Online file backups are big business these days.
Also, it’s not a good idea to rely on online backups as your only backup. Be sure you have a local backup on a hard drive or disk, because online backup companies don’t have a perfect track record, and your online backup can be lost or damaged. It doesn’t happen very often, but it does happen.