Loadedinc have a preview and interview with Senior Game Designer Hal Milton who is working on Microsoft's MMORPG Mythica:
The private realm areas or 'Playscapes' as they are called in Mythica intrigued us so we asked Hal how these actually worked:
"We have a storyline that takes place across the continent, and these private realms are within the land mass. We usually have them set into areas where you'll see a distinct barrier or gateway in. When you actually enter it's a seamless transition into that zone, so it's never going to stop to got to a load screen then suddenly you're in a different environment. You can see this dark shrine for many miles away on the terrain, it's like seeing a roller coaster at the end of the park, and you can walk to that element and then eventually enter the private realm and we give you the goals that you can uncover. Also, based on your party's composition, there are secondary and tertiary goals that we will unlock or hide. You will actually get many different experiences based on who you adventure with.