It's a great thing to do!! And it will definately be worth it!
I've had
many, many transfusions in my 16 years of life so far. And will probably have more in the years to come... But when I get blood taken at the doctor's (which is a lot... Once a month for now, was every two weeks, and before that two-three times a week

) it doesn't hurt that bad. Yeah, the pinch hurts, and if they fish around that hurts, too...

But it isn't so bad, you get used to it.
Since I have Wegener's Granulomatosis, a rare-rare autoimmune disease (normally rare, but even rare-er in kids), the doctors have to watch my blood levels constantly. I probably won't be able to give blood ever. Not that I really wanted to anyway! lol