From the sounds of it, they're both what conferences really should be . . . you collect people interesting in a particular topic, and then create an open space technology (the When and Why? section on this page is key . . . ) type atmosphere. From the first link:
Open Space Operates on Four Principles and One Law
* Whoever comes is the right people.
* Whatever happens is the only thing that could have.
* When it starts is the right time.
* When it's over, it's over.
These principles are simple statements of the way things work. While they may appear counter-intuitive to some, they are my observations of what always happens when people interact.
The one law or rule is called The Law of Mobility, also known as The Law of Two Feet. The Law of Two Feet says to stand up for what you believe and if you feel you are neither contributing nor learning where you are, use your two feet and go somewhere else. The law is fundamentally about personal responsibility. It makes it clear that the only person responsible for your experience is you.
I'm a big fan of open space . . . while it's a huge change from standard meetings/conferences/retreats/etc, the gamble seems worth the risk to me of it failing. The board meeting I was at last weekend is a perfect example of where open space would have made things smoother - lots of conflict, strong passion, and a president who was trying to lead when he didn't have buy in - which just isn't going to be productive . . . a leader can try and force things, but unless they build a structure which encourages people to have something invested, the organization isn't an organization - it's the leader's minions . . .
Steph K. was telling me about how at VISTA Leader's training they did open space, and one of the sessions that someone decided to run was on the NFL pre-season. While some might argue that such a session was ineffective and a waste of time, I'd play devil's advocate (as always) and say that it obviously wasn't - the people who chose to attend that session needed a break and saw no value in any of the other sessions . . . they applied the Law of Two Feet and decided that the session that worked best for them was a session that let them change gears and recharge for a bit . . .