This is yet another reason why I encourage healthy people in the US to get on the National Bone Marrow Donor Registry. It's extremely rare and very lucky to find a close tissue match outside of your own family.
I've donated via PBSC, to an anonymous at the time recipient. Call this tooting my own horn, but whatever, I figure I can offer a perspective from the donation p.o.v. In the relative scheme of things, the worst of it is a matter of time, and Filigrastim/Neupogen makes you feel like you've got the worst case of flu in your entire life. Your bones ache for about three to five days, you feel exhausted. I was aware of every bone in my body. However, I wouldn't call it PAIN. Discomfort, yes. Pain, no. I've got it on good authority that actual marrow donation is about the same: deep discomfort in the hip, but it only lasts about half a week to a week.
There are good reasons to not donate, hell, I'm now on the permanently deferred list, due to the discovery of some of my own health issues. I'd do it again if I could, but simply can't. I can see why people wouldn't want to, or just can't. For those who can, I really do encourage them to think about it. I count it as one of the best things I've ever done. Five years later, my recipient is a healthy 19 year old, off at college, and becoming more and more like a younger brother and pretty good friend.