What are you waiting for?
I don't get along very well with needles, but this is kind of, you know, important. And it's fairly unlikely that any particular donor will be asked to donate. Tissue matches are very specific, which is why it's so important to get lots of people in the database.
If you are Asian, or any sort of nifty minority, then it's extra important that you sign up. If you are mixed race, then it's very important.
Mimi lost a friend to cancer this year because they couldn't find a marrow match. There could have been one more name called at her graduation if there'd been just a few more biracial hits in the marrow database last year.
Look at it this way. Superman saves people all the time, but he has to go through all sorts of bother and trouble with the secret identity and such. A few days of lower back pain seems like a pretty awesome deal in comparison.
If I'm ever asked to donate marrow, I'm getting a cape.