A quick update on my first Regus attempt. I went to the facility at Rockefeller Center (1230 6th Ave, NYC) and had no problem getting in. They actually didn't ask for anything, which I assume was just the receptionist flaking out.

The down side is that the "free internet" in the "lounge" is a single wired jack at an easy-chair around the corner from the kitchen/lounge. Apparently people are known to reserve the chair here, so this isn't a great option for a random drop-in to get internet. At a minimum, call to see if the chair is available, and be ready to sit in the hall to use it.