Ok, my apologies if this has already been posted, but I was irritated when Marriott removed the comments box from the reservation process when they switched to the new booking process awhile back. I always used the box to request a specific room or area in the hotels that I frequent, and even had Marriott CS tell me to note in the comments when I was using an EEO rather than calling as most agents don't know what they are and all they do is add a note to the reservation in any event.

To add a note, after you are logged in and at the final screen before actually confirming the reservation (step 3 on the progress bar), click the pencil icon next to guest information and it will take you to the area you can add in comments, select arrival time, etc.

If you are not logged in, this box comes up in the reservation process, but since it auto fills everything when logged in you never stop at this screen during the reservation process.