Interesting article - I can't wait to see how this evolves. Second life is still growing rapidly - their users have lots invested in their virtual lives (especially financially). i don't think they'll up and migrate to another platform quite so easily.
They highlight 5 laws for companies participating in the virtual world:
1. Virtual worlds are not games, but neither are they a parallel universe (yet).
2. Behind every avatar is a real person.
3. Be relevant and add value.
4. Understand and contain the downside.
5. This is a long haul.
I still think our Cheil top ten rules are better (tom has it on his blog). Check out the full Gartner article here.