One of the coolest things about the new user contributions feature is wiki editing -- you can actually put up a map and have your community edit it like they would a text-based wiki. As the map owner, you can moderate all of the contributions.
This is a difficult concept to explain in the tool itself, especially since we're trying to avoid clutter and keep Atlas super-clean.
To demonstrate the difference between the two types of editing, I'm posting another version of the Northeastern University map I posted on Tuesday. The one in today's post is identical to the one in Tuesday's post, except wiki-editing is enabled (this option is listed under "Edit Map Properties").
If you click "Contribute to This Map" on the map in this post, you'll see you can click on any point on the map and edit it. In the map from Tuesday, you can still "Contribute to This Map", but you can only add points. You can't edit existing points.