Once it's built, though, we've created something of a monster. Habits are hard to change - just ask anyone who's taken up an exercise plan, or tried to quit smoking! So this means that now you've trained your audience, you have to ensure consistency. The message will change, of course. Over time it will morph from some variation on "in progress, have questions"to "finding some issues and working through them" to "done! hurrah!". But...
The medium must always be consistent.
If you've set an email precedent, stick with it. If you've set a wiki precedent, stick with it. Whatever habit you've made, you need to keep it.
So... we have achieved stasis. Forever and ever and ever... right?
Not exactly. Over time we can't simply keep doing the same thing. New people, new projects, new technologies - life moves on. And part of that is how you communicate, the medium through which you provide your message (10 years ago, a twitter project update would have been unheard of!).
If you need to change medium, choose a psychological break point.
Habits change at break points. Someone starts exercising after a heart attack. Someone else quits smoking after the cigarette tax doubles. These are break points, inflections during which people are more open to change. Find these, and use them to make your change. Start of a new project is perhaps the easiest break point to change medium. Staffing change or "process improvement initiative" is another.
As you communicate, remember, your audience values consistency. It's that consistency that lets them create a heartbeat for communication, and that lets them look beyond the medium to the message. Give them what they want, and you'll greatly improve your chances of getting what you need.