Hi H.,
I was an ovum donor twice in the past, so I just wanted to tell you about my experiences. As far as family background goes, if you work with an agency (which I did), you'll need to submit a LENGTHY family medical history as part of the application process. Even if you don't go through an agency, I'm sure that the clinic would require it. By the time you're done filling out everything they ask of you, the intended parents know you almost as well as your own parents do!
That being said, the agency I worked with did ask that I just keep my current email address and/or physical address on file with them for the next 18 yrs, so that if the child(ren) did develop any illnesses (which might be genetic or require a transplant) I could be reached.
The amount of contact you have with the parents, if any, is entirely determined by them. Some don't want any. I made it a condition of my donation that we at least have a lengthy phone conversation, since I didn't feel right donating to people I knew nothing about. But sometimes they don't want much contact. I also had to expressly stipulate in the contracts that the parents agreed to notify me if the IVF was successful; usually you waive the right to even know if they got pregnant, but I just couldn't live wondering, you know?
So there it is, short story long, LOL! Let me know if you have any other questions, I'd be glad to chat. It might not be the best decision for everyone, but I found it to be an incredibly fulfilling experience.