Checkout this article.
http://www.pointlesswasteoftime.com/games/wowworld.html
Where do you think jME will fit in this evolution?
You gotta like the PWOT style
MMORPG's are the spawn of evil 
I've got a few friends that I havn't heard of in a very long time as they've completely disappeared into the world of warcraft…
I've been doing a bit of exploring in SL.
You can check out some of my virtual travel snaps here:
http://www.sluniverse.com/pics/Default.aspx?Name=Komuso+Tokugawa
I'm also involved with the InnerLife project:
http://gaeacoop.org/cgi-bin/InnerLife/index.cgi
There are some interesting social and economic experiments going on in SL (in addition to the schizophrenia hospital and cerebral paulsy/emotional healing islands).
eg: http://www.theport.tv/ is a new entry from sweden…the live concert this friday should be fun, and their take on using rapid prototyping technology to make real worlkd products from SL developed content is an interesting twist.
Also the Second Life Relay: http://slfuturesalon.blogs.com/
In terms of open source alternatives to SL check out:
http://croquetproject.org/
and the java based:
http://muppets.rit.edu/muppetsweb/about/index.php
tip…don't underestimate the amount of work necessary to build and keep one of these things running with an ansty user community:-)