Just to gain a bit of perspective on this forum, I would never put anything 'critical' on to a PC or a Mac unless it was backed up. Doesn't matter what technology you're using, a hard drive is a hard drive and whether you're using OS X, Windows XP or Vista, Linux or MS DOS as your operating system, if that hard drive fails, you've lost your data (unless you have contacts in the hard drive recovery business, or a lot of money to spend in that business).
In all honesty though, I've so far not ever found anything I've ever needed critically which I can store on any hard drive so I don't worry about it too much. Yup, if my Mac hard drive died, it would be inconvienient, but I really can't think of anything truly 'critical' which would ever be on there and, even if it was, it certainly wouldn't be the only copy I had!