I have never personally donated eggs. I have a friend who did and she said the procedure was a hormonal roller coaster. The actual egg retrival will not "hurt" as this is done transvaginally. It's the preperation that hurts, let me explain. In order to have the best retrival you will be asked to take fertility drugs that cause multiple ovulation, thus allowing you to make several eggs for retrival.
These drugs can cause quite a hormonal shift since it's an overload of "girly hormones". There are few major side effects that you should familiarize yourself with so you can be aware of things like hyperstimulation (google it). Other then that as long as you can live with the egg donating process (emotionally) then its realativley painless.