When in doubt, lock the customer out
During my unpleasant stay at the Boston Marriott Copley Place, I:
- returned to my room after the second of a two-day-long conference to find staff had deactivated my keycard one day early. Why? Because staff declined the card I had on file after they tried to contact me all day--via the phone in the room I could no longer access.
- discovered, after a quick call to my bank, that Marriott had never attempted to charge the card in question, but in fact, had placed a $1 hold on my account and called it a day. Staff's response to me via the hotel's help line?: "Whatever. You'll need to come to the front desk." Click.
- was led by the MOD and a security guard through the lobby, up the elevator and to my room like a criminal (in front of fellow conference-goers). 
- was never issued an explanation or an apology. I was, however, greeted with watchful eyes as I left the lobby for the evening.
In short, if you want my experience--carrying a feeling of unwarranted shame, and fear that you may not be able to access at any given time the room for which you were charged TWICE--by all means, stay in this hotel.