Greengal,
I have been/am in exactly the same situation. After 4 months of research and soul searching, and being on the brink of going through the process, I realized that this is not a good thing for myself or my family.
The long-term effects of the drugs on donors, recipients, and children are completely unknown. As I'm hoping to have another child, and I don't have much time myself (being in my late 30s) I just couldn't feel good about the process. I might have felt differently if I had time to complete my family first.
My main advice for anyone in this situation is: don't try to do anything you're not happy to do. And don't let the situation drag out. Because I care for my sister, I tried to go beyond my capacity,thought I could do it, backed out, and ended up damaging my relationship with my sister very badly. However I don't feel guilty or regret having decided against donating. Though I want my sister to be happy, it was disappointing that she hardly considered my welfare (I know she is afraid to know the downside of IVF, so she has done hardly any research.) I know that if she tries, she can have a child without this kind of help from me-- anonymous donation or adoption are still options for her.
There is a possibility that "natural cycle" IVF (no drugs to stimulate hyperovulation) may become available in the near future. If you do a search on natural cycle egg donation and you'll find an article about a successful birth from this procedure done last year.