Here's how I think everything works and how Henry, Regina, Gold and Emma fit into the time issue.
Okay, so the curse happens. Time stops for the cursees, so no space either. They don't exist in a physical Storybrooke, but their conciousness exists, and does so both in an individual sense and a collective sense. That collective consciousness IS Storybrooke for the cursees. On an individual basis, the curse causes each person's consciousness to take their memories from a time when they were particularly unhappy, and twist that memory into a new version of their pasts, like a funhouse mirror for memories. So Ashley remembers she owes Gold her kid, because that's what was her unhappy time as Ella, Mary Margaret remembers she can't have love beacuse that's what was happening to Snow at her low point, David remembers he was committed to a woman he doesn't love, as James was at his low point, etc. Because James was unconscious when the curse hit, the memory didn't take till he came out of his "coma" and it was slow to take hold, but it still worked the way it would have from the start had he not been unconscious. They have a consciousness of certain professions, but no detailed knowledge of those professions, which is why once they get into the physical world, they will suck at any job requiring specialized or modern knowledge, like medicine or law enforcement or kid-from-mine extraction. Prior to time starting, none of their interactions with each other are happening in the physical world, but instead happening on the level of extra-corporal consciousness only. It's not a physical reality, but it is a reality, and they don't know the difference anyway.
Regina, Gold and Henry aren't subject to the time stop and therefore exist in physical space. But they and Emma each also have a connection to the cursees, either by knowing them in Fairy Tale Land or being related, so they are part of the cursees' collective consciousness. Therefore, they can slip into and out of the cursees' reality and interact with them in the realm of pure consciousness. They don't even know the difference - our perceptions are our reality. Or as Henry put it when Emma told him believing something doesn't make it real, that's EXACTLY what makes it real. Or to put it another way, the are separated from the cursees' reality by a veil so thin, they don't notice when they pass through it. Anyone who isn't connected to the cursees can't go to Storybrooke, because they can't connect to that collective consciousness. For those people, it's more of a (metaphorical) steel wall than a thin veil between the worlds.
Time starts for the cursees, and so does space, and so the cursees' reality now manifests physically. Now Ella/Ashley can have her baby. A FedEx guy can bring Emma her Sonic Youth albums. Good scotch and real Honeycrisps can be delivered. Gas prices are low, but that's a function of low demand, since the cursees still can't leave town. The curse has lost it's hold on time, but not it's hold on their psyches, as expressed through their false memories.
Gold, as the creator of the curse, he knows exactly how it works on every level, and designed it so that he could always do whatever he pleases. So he can come and go between Storybrooke, Fairy Tale Land, and our world at will and that's how Henry got there. Regina only understands the curse in broad strokes and only cares anyway if it pertains to her objectives. She could probably go to Paris if she wanted to, but it wouldn't occur to her. Storybrooke is her realm and its people her obsession. Paris isn't real to her. Henry can obviously leave, and I think Emma can, too, but she has to believe she should, and she has to keep her eyes on the damn road so she can see wolves just standing in the road. The curse has a pull on Emma to stay and play the hero role, but she could choose to reject that role and leave if she truly wanted.
Edited by ViciousCircle, Jan 13, 2012 @ 11:45 PM.