Current regulations mean that if you've received blood in a transfusion or any other procedure since about 1984, you are ineligible to donate.
I have, so I can't.
I can only echo the OP - if you can, then do.
I can't, but its thanks to people who do that I'm here at all. Ironic really that its the fact that I have received the benefits of blood donations that prevents me from returning the favour, but there you go.