Imagine you have a successful mailing list/newsgroup.
People subscribe once to whichever groups they like and then receive e-mails when someone posts to the group.
The community comes to them. It's inserted into their existing habits. They don't have to go to the community.
This is a powerful thing. It's far harder to make someone regularly visit a community platform every day than to check their e-mail every day.
This isn't to say you can't create new habits. When did visiting Facebook/Twitter/our daily news sites become a habit? It does however have some key implications.
First, there is a huge opportunity to insert the community into our existing habits. If we get an update about the community when checking the platforms/tools we use every day, we're far more likely to be a a regular community participant. E-mail, Facebook, and Twitter are powerful platforms to let people see when their is interesting activity happening in the community.
Second, be careful about assuming people will change habits. We recently spoke to a community manager whom moved from a mailing list to a community platform. The platform was much better. The level of activity instantly plummeted. If the new habit is harder than the old habit, you're going to struggle.
Third, you can create new habits but it takes time and skill. Newcomers need a series of very timely and relevant prods that keep them visiting the platform to see what's new. This is a process of optimization. They need to feel that this is their peer group and they satisfy their social needs by seeing what their peer group is doing.