If you have not signed up for Dropbox and tried it out you do not know what you are missing. It is by far the best online backup service available. They give you 2GB of free space when you sign up for your free account. They have applications that will work for Windows, Mac, and Linux machines. The software creates a folder that you can drop your files in and they'll be automatically stored online.

Anyway, really the only way to really get it is to try it out.

I get 250MB extra space for every user that signs up under my referral link. I am currently at 4GB!