Umm, back up the whole thing? I would really not recommend that. I have an 8gb thumb drive, and 8gb iPhone. I also use <a href="http://zumodrive.com" target="_blank">ZumoDrive</a> which is a cloud storage service. You can sign up and get a 1gb free of storage. Good for your .mp3 and .jpegs and some blank DVDs. They all do the job for me well, however the way I backup my whole computer takes me a at least 24 hours I know it is the safest way. I have 30gbs of Adobe AFX footages, Soundbooth medias, and a lot. I format my computer almost every other month.
Here is what I do. I have partitioned my computer into 2 piece, just so I can have my Hackintosh running whenever I wanna work with .php files. The reason I mentioned it is because "when you want to format" like double clean up your whole system you will need to do something like this! Just so your registry entries would't be left and be loaded even after you format your computer. Zip up everything you wanna (takes time, but highly recommended!), save them somewhere safe like flash cards and dvds, DO NOT insert your Windows 7 (applies to all versions of Win), insert some wrong boot up DVD, like Hackintosh. Or Linux. Let their Disk Utility clean up your whole thing! That is the only way you can have your computer last long enough. I have Dell XPS 410, with some good and upgraded ram, better cooling system etc and I work with lots of Media, lots of Photoshop and heavy /localhost. Which means I must have at least 5 to 10 things running whenever my computer is up. They are storing every little data of you on your computer. You'll be surprised!
Well, after all it's just my way tho. Slow, lots of work, forget something sometimes... But well worth