This happened to myself and a friend on New Years Eve.
I booked the Fairfield in Woburn, MA under my name, credit card, and MR number for a 10pm check in. My friend was driving up from Philly and arrived much earlier than I was able to get there. He had the hotels confused and tried to check in at the Courtyard Woburn, at which point they told him there was no reservation there under my name and found the one at the Fairfield. They called the Fairfield to let them know he was on his way and once he got there, they checked him in without asking for ID or credit card, they even gave him my elite welcome package!
I was infuriated when he told me this happened! What if he was a crazy stalker and hacked my e-mail account and got the reservation info or something??
I never put him on as the second party, so there's no reason, in my mind, why they should have allowed him to check in.
What's Marriott's actual policy on this? Anyone know?