Justin is right, insofar as specific behaviors need to happen in order to maintain the integrity of the protection an LLC provides. I'm not a lawyer, but my understanding is that one good example of this is the need to keep corporate funds and personal funds separate--if you use LLC funds to pay personal expenses or vice versa, your LLC may not do much to protect you or your family's personal assets if you're sued.
I take a very different conclusion from this, however. Rather than give up and say its too much effort, my non-legal recommendation is to learn what you need to do to maintain the integrity of the LLC, and then do it.
One lawyer specializing in asset protection said it best: insurance and corporate asset protection are different things and a wise investor uses both to minimize exposure to severe financial risk.
Here are two links for more information:
http://www.nolo.com/legal-encyclopedia/llc-basics-30163.html
http://www.lonestarlandlaw.com/LLC-Formation_in_texas.html
David
PS: I've never heard of a case where the number of owners in an LLC had any bearing on how effective the LLC was in offering asset protection. Justin, can you please provide a reference so we can do more research?