The PairVine is the way a lot of project learning happens in an ExtremeProgramming project.
Someone learns a cool thing (could be an approach to coding, a way to use a tool, an approach to a design problem, etc.). The next day (or later in the day), when pairs switch, the cool thing is shared with someone else. They tell two friends, and so on.
Before you know it, the cool thing is in use by everyone. No meetings, no voting, no dictates, etc.
If it isn't really a cool thing, it gets shot down before it goes too far ("no that's not a good way to do that, this is a better way"). Often, it gets tweaked along the way and eventually comes back around to the person who first found the cool (and now even cooler) thing.
Wonderful communication through an informal network. And progress didn't slow down for a minute.
-- KenAuer