I used to donate pretty regularly, even with a girlfriend at the time who fainted when she tried to join me in donating one day. :)
When I lived in Wichita, I donated very regularly, my boss and I would donate over our lunch breaks. And then one day, I got a letter from the local chapter of the Red Cross.
In order to protect the blood supply, they told me they'd had to destroy a second straight donation from me, because one of my liver enzymes was a little high.
It said I should check with my doctor as it's probably no big deal, but several things might cause that... turns out my doctor confirmed it was no big deal.
My primary concern at this point, Why didn't they tell me after destroying the first donation?
And then there's all the negative publicity they've had about being bad stweards of donated moeny, PR-focused, and so forth. I'm just done with them.
Transparency needs to beome a byword for these folks. Until then, I'd discourage anyone from giving them anything... time, money, or good pr.