I became a blood donor couple years back when i was medical student. My friends was well established donor and he talked me into it. Since then I have donated my blood 10 times.
Most hospitals and transfusion centers are always in need for blood so if you can do it I encourage you to start doing it.
It goes beyond helping others. It's very healthy for yourself too. That's karma I guess :)
Blood donation reduces iron in our body which is very chemically reactive metal and creates a lot of free radicals that do damage in our cells. Especially in men since men don't lose portion of their blood every month. This way you reduce your iron levels and keep yourself healthy!
go out there and help yourself and others !