O+ - 31 years old and I have donated 13 times or so. In Ireland, you are only allowed donate every three months and I have been refused a few times. Once I came in 3 days early and was refused again for three months! and other than that, low iron. Also, a few times, I couldn't cause of travel, including to the US (west nile virus?) I got a lovely letter from the transfusion board though saying "we know how disappointing it is that you couldn't donate..." and it was true. For me, it was one of the few things that I did for others and it meant a lot to me that I could do it. I used to take a Friday off every 3 months or so to take the trip home and built the donation into that time.
My flatmate's girlfriend was asking me recently about donating (her first time) and we are going to set up a time to go together. When I arrived here (Australia) first, I applied and they had too many people so asked me to come back in a few weeks! Between having a sore throat etc, I couldn't recently, but will go before my next root canal (ugh). I think it does help people to go with the pros
I've had a few people come with me before and I do think it helps them not be scared. And there are usually snacks!