When I gave away some of my ADR's, I worked on the swap board here. We sent PM's to exchange names, and I called the ADR line and switched the name on my ADR confirmation number. Once it was secured in the new name I PM'd the person with their confirmation number and a reminder of the time/date/place of the ADR.
I was not comfortable with just giving anyone my confirmation number. Confirmation numbers tie to reservation numbers, home phone numbers, possibly credit cards, and it was too much personal information for me. I have some very good friends in the internet, and believe that people are inherently good. That being said - I am too cautious to potentially give that much information out to a virtual stranger - even a friendly stranger. In the day and age of identy theft, credit fraud, etc I belive in being more cautious.
Most wouldn't abuse the information that they were given, but some may, and you never know who is on the other end of the keyboard.