sadie42 beware long post!
We had treatment with donor eggs, which was unsuccessful. We have contemplated more and I have heard good things about Spain. Not sure yet which route we will take.
Before starting on the donor egg route I decided that I would definitely want to tell the child (if there were one) that they were conceived with a donor egg.
I think what you decide to do regarding telling the child will possibly influence who else you tell.
My understanding is that this kind of information if drip fed to the child over a number of years is just part of their story and is therefore not a shock or strange to them. The Donor conception network may be able to advise about how to tell etc.
However, if you do not tell the child then it would be a secret you would have to live with. The more people you told the greater the chance that the secret may come out. I think that for a child to have grown up believing one thing to be true and then to find out something else is true it could be a shock and could damage the relationship, though I am not sure much - I'm not being a scare-monger but just think that it is easier for kids to know this all along.
Everyone is different but personally I would not want to have the chance that the information could come out one day and change my relationship with my child. I also think that it is in the child's best interest for them to know. That way they can know as much as possible about their medical history etc (which would be different from yours). Once I had come to terms with the idea that the child would not look like me etc it was actually something which I felt very comfortable with. Lots of birth children look nothing like their parents.
Exactly who else to tell is obviously your choice but personally, I chose to tell my mum and sister about treatment and had we been successful I would have told all our close relatives. Again, for me, I think it would be hard for close relatives to think that the child was genetically related them and then find out that they were not. Where as if they knew from the beginning then the relationship would bloom and blossom naturally with no secrets.
Having said this, there is no need to tell everyone and obviously once you tell people you can't un-tell them so I would be careful not to tell too many people especially people who you are not happy to tell.
I wish you every success with your path, whichever you choose. Please do not be put off by the fact that our treatment did not work, I know other babies born by donor and they are lovely and one does actually look like her mum.
There is even some suggestion that a woman's womb may turn on or off certain genes so could influence the outcome of the baby anyway even if born from a donor egg - this is not certain! Just read it on the Internet.
Whatever happens hope you feel peaceful about your decision and are happy.