Posterous, a blog service that I've written about in the past, recently made some changes to their service that educators should be aware of. First, the name of the service is now Posterous Spaces to reflect the fact that the service is designed for groups to share content with each other publicly or privately. Second, now when you create a blog or "space" with Posterous you can make that space public or private. A private space can only be viewed by those people you specify in your administration panel. Likewise, you can control who can and cannot comment on your blog's posts. You can maintain a mixture of private and public spaces within one Posterous Spaces account.
One thing that hasn't changed about Posterous is that you can still allow people to make contributions to your blog by simply sending an email to "yourblog'sname" @ posterous.com. You can choose to moderate or not moderate those contributions. From an administrative standpoint, using the email method of contributing to a group blog is much easier than having to enter permissions for each person you want contributing to your group blog.
Here are two videos explaining the new Posterous Spaces features.
Introducing Posterous Spaces from Posterous on Vimeo.
What's new and what's different about Posterous Spaces from Posterous on Vimeo.
Applications for Education
As I mentioned above, you can have people contributing to a group blog using Posterous Spaces without having to create usernames and passwords for them. Simply have them send an email to "yourblog'sname" @posterous.com and their posts can appear on the blog. It's the quickest way that I have found to get a classroom full of students contributing to one blog. In fact, this is the method that I am using in my Global Studies course this fall.