I haven't read this entire thread yet, but I'm sure glued to the computer! I had to post after reading about room cards being programmed with the same codes for different rooms. This happened to us, off-site at DL. A very nice hotel though.
DH and I were asleep in our room with DS2 and DS6months at the time. The baby was in a port-a-crib near the door, as that was the only space for it. DS2 was in the bed by the window, and DH and I were in the bed next to the crib. I don't know what time of night it was, but we were woken from a deep sleep by the door opening. Two men, obviously very drunk, walked in talking. Their hands were resting right on the crib, with the now crying baby in it. I was terrified, having no idea what was happening. Thank goodness DH went into protection mode, and jumped up, insisting they leave. Since they were so drunk, they were confused and insisted it was their room. DH just kept saying VERY firmly for them to just GET OUT and go back to the front desk. After a few minutes they did, with no incident. We called the front desk when they left and alerted them that someone was able to get into our room. When we checked out the next day we found out our room had been double booked, which is why they came to our room in the first place. It had never been marked on the computer as occupied. Since I was so tired, I remember at the time I was mostly annoyed that they had woken the baby (anyone with kids knows how hard it is to get kids that age all to sleep in a small hotel room!). In the morning however, I was very upset when what happened fully registered. Everything was fine, but considering how drunk the men were, I don't want to think about what potentially could have happened.
So it does happen. I think that's the most shocking thing to happen to us in particular.