The basic idea is that you build a community and live there. Each family own their own unit, but there is a lot of common facilities used for group functions. You can often get away with smaller units because things like guest rooms and party spaces can be shared. It is an intentional community; both through design of space and explicit community building, you get people to want to spend time together and to work together.
I like the community aspect a lot. That's good: cohousing is clearly not worth it unless you do. You end up putting in huge quantities of time and energy —far more than you would even if you bought a house on spec. However in addition to a house, you hope to get a community that works well together, where you could raise kids, help others, ask for help, and work together.
At this stage there are still a lot of questions in my mind about whether this particular cohousing community will be right for me. They are fairly early in the process. They seem to do an excellent job of community building and have basic organizational structures set up. However they need to pull in new skills and people to actually pull of a project as large as a community development. Also, a lot of decisions remain to be made and there is no telling if the ultimate result will be right for me.
But hey, I needed another big volunteer project! I don't have enough to do.:-)