Over at Dusan Writer's Metaverse, there's an interesting taxonomy discussion going on, about what Prokofy Neva quotes as "a business need to quantify and measure the spaces.” There's the useful Metaversed definitions, but Dusan also tipped us off to a taxonomy made by Lag-O-Rama, excerpted here:

MMP (Massively Multi-Player) - a mostly non-instanced online game, with only a few instanced areas (such as raid zones, etc). Examples: World of Warcraft, Everquest II
IMP (Instanced Multi-Player) - a mostly instanced online game with central non-instanced social hubs, where players can restock, meet up, form groups and socialize. Examples: Guild Wars, Hellgate:London.
Lifesim - a virtual world with no real “game” incorporated into it. Examples: Second Life, There, the upcoming Twinity.
Gamehub - a collection of casual games held together with a social setting hub. Examples: Zwinky, Neopets.
Dueler - primarily a head-to-head online multiplayer game, where the online presence is there, but practically no social setting exists…it’s all about the combat, baby! Examples: Gunbound, Yu-Gi-Oh Online.

As you can see, Lag-O-Rama's list seems, largely, most useful for MMORPG players, which takes us right back to the beginning of the issue -- how different are MMORPGs from virtual worlds? Some can be quite different, like Hellgate, and some are not very, like Entropia.

Dusan has made a very interesting content map (shown, full version here) which is useful -- at showing how many different categories and classifications there could possibly be! Unfortunately, this quest for taxonomy will probably persist for a while yet, because of the role of enterprise and investors in the space. And Dusan provides a great translation of investor-speak:

Here’s how I imagine a pitch to a group of bankers or investors who know nothing about virtual worlds:

“We’re going to create branded entertainment products and aggregate social communities by creating a Web 3.0 space that leverages best in class talent incentivized with virtual currency. Investment in this opportunity is high risk but the risk:ratio return is high because we will establish best practices and aggregate eyeballs within the social/entertainment Web 3.0 space towards creating a portfolio of opportunities for future monetization.”

Here’s what it really means:
“3D stuff is really cool. We really have no idea where this is all headed. We want to take a gamble on creativity, passion, collaboration. We’re going to work with some Neko who hangs out at the Missing Mile and a Gorean Master who also runs an erotic strip club for furries. We figure we’ll throw a bunch of prims together, hope we don’t get griefed, make some cool stuff, and have some fun - and if we can do all that, a whole bunch of people will probably hang out, become friends, and our passion will spread, and some day that whole thing might make us some money or it might not, but we’ll probably survive, we’ll learn a thing or two, we’ll for sure end up with some possibly worthless real estate, a bunch of code, and some objects that we’re just as likely to give away as sell, and hey, maybe we’ll become better human beings by learning to work with each other in a different way, and to help people experience emotional, immersive evnironments in new ways.

Yes, it's funny, but salient! Writer's full piece on the issue is here.