The system and revenue model is markedly different from SL, however: instead of fostering user-created content in a single world, Multiverse is a network of worlds accessible by the client software. It comes with e-commerce tools built into the system, so developer's can earn an income, while Multiverse makes money by taking a 10% cut of that revenue.
I haven't yet had a chance to check it out first hand (the client is cantankerous with my Vista machine), but I'll be keeping a close eye on its progress. Multiverse's advisory board includes Avatar director James Cameron and some other Hollywood heavyweights, so you have to think movie-to-MMO tie-ins are planned. (Indeed, a Multiverse version of the cult TV show Firefly was announced last year.) What's more, famed MMO academic Ed Castronova is already using Multiverse to develop the education-oriented MMO Arden.
My writing career has been tied up in Second Life on one level or another since 2003, so you might think I'd consider Multiverse a threat to my livelihood. Actually, I'm relieved. There are some truly impressive and popular mini-MMOs built within SL, like City of Lost Angels and Midgar, but they've largely succeeded in spite of Second Life, which is still far from ideal as a platform for game development. It's never healthy for any one company to dominate a space for so long, and an active competition to attract and retain new users and developers can only benefit us all.