I'm a tough case; my veins are small and deep--and this was true when I was six years old, before burying them beneath extra padding, and it still holds true today. My phlebotamist was a dear; after much poking and prodding she was honest in her worries that it was hard to find a vein, very concerned about my comfort as she poked around, and triumphant when we succeeded, admonishing me with, "Don't you dare move that arm one bit!" Three bags and six tubes later and we were done.
I'm a big wuss when it comes to pain, and especially hate needles. Even with her having to poke around a bit once in, the pain was no worse than a minor bee sting; she kept asking me if I was okay and I'm thinking, "About what? This is nothing." My biggest pain is a forearem strain because I was SQUEEZING when she told me to in hopes of popping out a big one for her. Seriously! No such luck!
Given the results (one donation can help three people!) it's a very minor sacrifice for a really awesome good.