First TimeWas last month.
Did it on an impulse, because I was bored and another guy from my old class was donating and he was asking around if anyone wanted to go with him? and that he'd go if anyone accompanied him. So i thought let's try this and went to the tent. They asked me stuff like what I had eaten for breakfast and was it my first time etc etc.. then I filled a form, then a bored looking doctor(who was reading Paulo Coelho I noticed) took my blood pressure and pulse rate and got alarmed at the sight of a wound on my arm, which, on a second look he realized to be a fake ballpoint tattoo(it broke my heart to see my creation being seen as a wound, actually :P).
But then I fell on a bed, they put a needle in my arm, filled a bag with my blood through a tube while my friends looked at my face upside down. Then, when it was filled, the doctor or whatever who was taking it, threw my treasured blood in a bin! I mean, I'd thought it would be more exclusive, me being the only person in the world who ever donated blood and all.. But oh well.
It's really easy and you don't feel anything at all and get free snacks! :D
Do try if you don't have anything stopping you.