I used to, but I've just been told to stop before TTC I have 40-something donations under my belt, so I feel good that I've been able to help so many.
Last time I went to do it, I was waiting at the bus stop, and this old dude tottered up to me and said "Are you going to the city? Can I offer you a lift in my taxi?" So his taxi pulls up, and he asks where I'm going. I told him it was to give blood, and he said "Well, how funny that we should meet. I'm on my way to receive a blood transfusion."
That made every needle worth it. Even the mega two-headed ones they use for plasma, over 40 donations worth of scar tissue.