For donating PBSC, you have to take filgrastim for a few days, which releases a lot of the bone marrow stem cells into your bloodstream. The effects of filgrastim aren't too bad at all; some people feel fatigue, nausea, a little achy, but I've never seen anything too bad. After donating PBSC, some people feel a little pain at the injection site, fatigue, and sometimes bone/limb pain. Donating bone marrow surgically is done with anesthesia, so you feel no pain during donation, but you could feel some mild bone/hip pain afterwards. There's been several studies, which I could try to dig up, that show there really aren't any long term effects of donating either marrow or PBSC.
I've been interning with a bone marrow registry this past summer and one of my jobs is monitoring donor recovery, and the most pain/effects I've ever seen a donor deal with was for traditional bone marrow donation, and they labeled their pain as "moderate." All of the effects go away within a week or two, and if one experiences true discomfort, there's a team of nurses specifically for bone marrow donors who can help ease any pain.
But, to each their own. If you specifically say you will only donate the traditional way, then the patient's doctor may accommodate, but sometimes PBSC is the best way to go because you can get more stem cells that way. Either way, by signing up for the registry, you're doing a great thing and I'd be happy to answer any more questions through PM so we don't derail this thread too much 🙂