The blood donation itself is taken from the arm, but the pinprick haemoglobin test they do to check your blood's worth taking is done on the side of a finger.
I usually give, though I'm currently on a one year suspension, as I'm about to be a bone marrow donor (see separate thread).
I am always so disheartened by the number of people who don't give blood. I am well aware that there are many who can't, for one reason or another, but the vast majority just can't be bothered, and when you think that you lose nothing for doing it, but can potentially save a life, that's just a plain unwillingness to give up half an hour every four months.
I used to goive blood, then started giving platelets which means a needle in both arms whilst blood is removed from one, platelets are taken out, remaining blood put back in the other arm; you get double points for it too.
I've given blood about 10 times, although I haven't done so recently I must admit.
I'm AB+ which is fairly rare (about 3% of the population). It's probably the least useful to the NHS though, as I can only give blood to someone else with the same blood group.
On the other hand, AB is called the universal recipient because I could take a transfusion from any of the other blood groups (provided the rhesus type +/- matches). It's best to match the blood group exactly though.
If anyone is interested in giving blood, you can find further information, including locations of mobile blood donor session on the website for the National Blood Service: