I would imagine that a pint of blood is quite quickly restored, which is why they only take a pint? you would probably have no lasting ill effects from donating.
I used to give blood until the rules were changed for people donating who had received a blood transfusion. This upsets me, as I received 6 pints of blood after giving birth to my first baby and will be eternally grateful to all those who give blood in their lunch hours..without whom I could have died.