You see, most of us are on asynchronous broadband links. ASDL, to use the full acronym. What this means is that home broadband is great for downloading stuff and not brilliant and uploading it. Upload speeds from the average connected home are or the order of 128kbps. This is just about OK for uploading short video clips to YouTube and fine for syncing documents up a web server, but it's utterly inadequate for being the basis of an all-in online backup solution.
The likes of Carbonite (and I'm not just picking on them, I've heard the same idea from others and from several should-know-better bloggers) say that you can just select folders of favourite pics, music and videos and they'll be spirited seamlessly up into the cloud, fully backed up.
Oh no, they won't. What'll happen is that you'll tag the aforementioned folders and they'll start uploading. And, three days later, they'll still be uploading. And in the meantime the saturation of all your upstream bandwidth has meant that everyone in your family has been just about locked out of doing anything at all online.
Don't be taken in by the hype unless you really do have a lightning fast non-ASDL connection - by all means back up your document folders and anything really important online, but stay clear of your media - that 80GB of JPGs, MP3s and MP4s is far, far, better backed up locally - to another (plug-in, removeable?) hard disk or similar.