Look, if you sign up, you sign up to actually give marrow if there's a match. Period. Unless you're not healthy enough, there's no excuse for welching on a deal that involves someone's life.
No it's not like a blood donation.
It's misinformation like this that cause people to sign up to donate, and then back out when they find out what they really have to do. Bone marrow donation is a surgery. PBSC donation requires you to get injected with a drug for 5 days, and then have your blood drawn out from one arm, go through a machine, and passed back to you through the other arm. If you have thin veins it'll even require a central line (tube in your neck).
This is why Flynn vs. Holder is so damn important.
If the goal is to actually save human lives, more people need to choose to let doctors invade their bodies to take the cells they need, take the time off of work, away from their goals, etc. The only way that most people could do this for a stranger is to be compensated. I predict great things to come!
I'm trying to think of a dollar amount high enough to let somebody stick a tube into my jugular and extend my circulatory system outside my body for hours. I don't think I can count that high; unless I needed the money for fairly immediate survival.
It's not as bad as it sounds, though 6 hours is quite a while. Platelet donation is done this way (http://www.redcrossblood.org/donating-blood/types-donations/...), taking an hour or two each time, and there are donors who make a platelet donation every two weeks. The blood cools while it's being run through the machine so you get chilly, but donors generally just sit under a blanket and read or watch a DVD for the duration.
It appears that there are two methods: 75% of the time it is PBSC, which is the 6 hour long blood donation. 25% of the time it is through surgery under general anesthesia. The doctor decides on which one based on the patient.
Up until today, it was illegal to seal the deal (i.e., pay your donor). Now that people actually have a rational financial reason to trade a little bit of their own lives to strangers (needlesticks aren't painless, and donors need to sit for hours to actually donate the cells), they'll go through with it a lot more. The donors win, and the recipients win. That's a great thing!