I would love to donate, but I have a needle phobia, and a history of fainting with blood tests. When I spoke to someone on the mobile unit about donating despite my phobia, they said they would prefer it if I didn't because chances were pretty good I would faint. I can't argue with that. I'd take up a bed for much longer than necessary and they'd have to stop the collection early. Better off getting people in who aren't going to cause them the hassle.
I've never had to receive blood products, but my dad has had multiple transfusions after a nearly fatal motorbike accident.