I was closing in on 10 gallons (80 units, right?) when I last was able to check on the mainland. Paradise blood bank now has me signed up for every 56 days until I am no longer healthy. I'll never catch Kahn, but it's not really about that. I feel very good about any contribution I've made in this fashion. Though one never knows specifically where the blood goes, I'm sure I've at least participated in "saving lives". That's enough to make it worth the effort and trivial amount of pain (once in a while).
An interesting story (well, you decide as YMMV): A female friend from HS (and from church - which is what makes it even more fun) became a phlebotomist in mid c*reer. One time when I was still w*rking, she and her co-w*rkers came to our w*rk site for a big draw. She was doing the health interviews for a while (apparently, they rotated duties from stickers to interviewers to packers to mini-physical takers, etc.). As anyone knows who gives blood, there are half a dozen or more questions about sexual history (an effort to avoid contamination of the blood supply with STDs - especially HIV). We were both professional about it, but we both had to stifle a chuckle and grin during the process.
Anyone eligible (and able) should consider this "gift of life". There is always a shortage of blood - sometimes critical. My understanding is that there is no upper limit on age for donors.