Your hard drive is going to fail. It is not a question of "if" it will fail, but "when" it is going to happen. If your drive failed right now, what would you lose?
This topic is especially hot to me as I'm dealing with a partially failed SSD drive right now (bad block). While this problem has cost me a LOT of time this week (my most precious resource), I have not lost any data or files.
I talk briefly about my backup strategy on my Digital Workflow page. There are many good ways to store copies of your data (including some online services), but the device I use most (and the device that saved me this time) is the Western Digital 1TB My Passport Essential SE Portable USB 2.0 Hard Drive (B&H).
I have 10 of these in my current backup rotation (along with many additional small capacity drives). They are very small (easy to take off site) and have given me no problems to date. The autorun software is a pain, but there are fixes available for this. I just turned off autorun.
This is the second primary drive failure I have experienced in less than two years. Backup what you care about!