UPDATE: Keith McCurdy kindly reminds me that "Personal scenes can be much larger than just rooms". Of course, VRML and now X3D are scene technologies and can be used to create much bigger spaces. My point is to emphasize the marketing of locales over very large and very expensive Earth map systems. A successful standard addresses the most common uses and they are locale-based. Scenes if you like. Islands if you like. Locales I like because scene means something different to me: it is thematic. Locales are organized as proximate space and proximity is king. Small is beautiful because you trade large spaces for rich locales.
Again, how much terrain is really practical given operations over it?
SecondLife to a musician is a gig. To a virtual artist, it is a canvas. Canvases are portable or they end up being site sculptures. Build it. Forget it. Tour act vs houseband.
The Deal: if you want to build a body of work in the medium, use VRML/X3D so you can take it with you. If you need walkthrough to sell other products or to be seen (basic nightclub), Second Life is the place to be. It's THE gig du jour.
However, if you building galleries and want access to ID'd customers with similar interests (aka, walkthrough), you want easy access so use Vivaty in Facebook. Why? Shared services. Vivaty isn't as service rich (eg, live streaming audio) but the Rascal Flatts premiere had excellent walkthrough.
Second Life's advantage here is it hosts live acts and has very large spaces to roam.
Vivaty's advantage is X3D integrates easily in mashups and the spaces are small by contrast. The question is, apart from the MetaverseShaggyDog, are large spaces practical in the sense of do you really need them? If you can trade-off continents for room, are rooms more practical for business and private meetings?
Worlds vs Rooms: Big worlds are fun for roaming. Small worlds are practical for chatting, shopping, and meeting in a room. Smaller worlds have their own beauty.
How often does the average web user actually use or need a 3D application with Earth-sized real-time terrain? I'm really asking if you have opinions on that question.
In Vivaty, it is videos and recorded audio which for a free service is excellent. Use their resources to put together a gallery. It's simple to do because it's drag and drop library widgets. Walkthrough numbers show a definite increase. It's advantage is integration with Facebook. So if say you already have maxed out 5000 friends on FB, you will have excellent walkthrough. If I were label sales manager, I'd look at this because it enables them to put their YouTube library, live recordings, other stuff in one easy to walk-around-room.
And like most web stuff, you can do multiple projects.
If you are one of the people in the music business still fighting this stuff, you're dead. If you are one of the people trying to figure this out so you can use it, happy to answer questions.