Ubuntu is not a consensus-based community. Consensus communities rarely work, and I am not aware of any Open Source project that bases their work on wider consensus in the community.I'm not entirely sure what he means with consensus and community here. He himself defines community as "a collection of people (or animals) who interact with one another in the same environment". Consensus decision making, according to Wikipedia, is:
"a group decision making process that seeks the consent of all participants. Consensus may be defined professionally as an acceptable resolution, one that can be supported, even if not the "favourite" of each individual"
Talking consensusLet me take this as an opportunity to address a common misconception about consensus: that consensus means full agreement. The Wikipedia entry already points out that the outcome has to be 'acceptable', one that 'can be supported'. This matters: Jono probably meant to say that there is no sizeable community where everybody fully agrees on every decision and I can't imagine he is wrong on that. But that is not what consensus means.
(dis)agreementThe reality is that in a large and diverse group of people, it is impossible to really reach full agreement on any sufficiently complicated matter. Making decisions on agreement of all participants thus doesn't work. Consensus, instead, allows a decision to be made even in the face of disagreement. Essentially, it is a form of democracy without voting.
Ever heard the phrase: "Let's agree to disagree"? That is it: at some point in a decision making process, consensus requires some of the participants to be mature enough to step out of the way and let a decision actually get made. And others need to respect them for that.
VoluntairyWhat makes consensus different from voting?
Usually, those in a small minority are the ones who have to (wo)man up and accept that the decision and project is more important than them. The main difference between voting however, where minorities (anything below 50%, usually) don't get their way, is that it is not mandatory. In some cases, the minority can get their way and it can be the majority which steps back and lets them. And even if that doesn't happen, the difference between being forcefully over-ruled and gracefully accepting that you can't always win is big.
A second key point is that ruling by consensus requires discussion, much more than voting does. You can't make decisions by consensus without informing people of the choices - you have to know what you (dis)agree with. Certainly, a community where a few take decisions without talking about it does not decide based on consensus.
Last, the two are not incompattible. It makes all the sense in the world to occasionally do an 'opinion poll' (as opposed to doing a decisive vote) to aid the decision making process. This is valuable input for a consensual decision: vocal supporters of either side can create rather distorted views on how strong the support for a certain opinion really is.
Trust and respectSo I think Jono is wrong when he states that there are no communities which decide based on consensus - KDE is an example of one, Gnome does it often and it's pretty much the way of the Geeko, too. Others usually prefer to vote (Debian) or have a more top-down structure like Ubuntu. There are many ways to Rome, as they say. Being aware of that is a good thing - and being dismissive of ways other than yours is not.
I want to add that Valerie Zimmerman made an excellent argument for the importance of trust and respect. No structure of decision making works without these - trust that those who disagree will have the courage to agree-to-disagree, trust that the majority is right or trust that those who decide for you make the right decisions. And respect each other while debating it.