A friend of mine participated in receiving an embryo adoption for implantation. She explained to me that it's not the same as what we think of as "adoption" as it is not an actual child yet, but frozen tissue. Of course peoples personal religious beliefs may challenge this. She was successful at achieving a pregnancy through embryo adoption done at her RE office. You sign some kind of legal paperwork stating that the owner of the frozen embryo is freely giving it to you via this process. The donating couple/person is usually relieved that someone was wanting to adopt since many people feel guilty leaving their frozen embryo if they have since decided they do not want to try to have any more children.
The success rate is fairly high too, since the embryo is from a group that had previously achieved a pregnancy. I think the success rate I was quoted was between 40-50% success. Also, for older women, this is good because the age of the people who froze the embryo is the age that it is, not the chronological age of the women it is being implanted inside.
Hope this clarifies some questions you may have had concerning this... ask your RE if they participate in this program if it hasn't ever been mentioned to you.