I donated yesterday morning at the American Red Cross in Camden, NJ.
[Tested through bikur cholim in Lkwd.]
Simple process, they try to get 650 mL of plasma [can take between 3 -5 rounds of blood filtering depending on your red blood cell count], but 130+ is enough for a basic patient.
No dizziness etc normally associated with donating blood, as all your blood is put back in you. Only hydration is needed, and they reccomend no alcohol or caffiene for 12 hours while the body rehydrates.