Here is a brief rundown of the advantages and disadvantages of posterous, tumblr, and wordpress for teaching.
Posterous is the easiest for having students sign up, because they don’t have to sign up. You can just enter their e-mail address and they will be able to post to the blog by e-mail and receive updates from the site. They never have to register unless they want to edit an already existing post or have access to the site without entering the password. (I always use private, password protected, blogs for teaching.) The problem is that for many students, especially those whose software or e-mail servers don’t properly support unicode (which is surprisingly still too common a problem) they won’t be able to post in Chinese text. It will appear as gibberish. Another problem is that the blog doesn’t display author names and avatars on group blogs, so it is hard to know who wrote what.
Tumblr has the advantage of looking nice, and there are features to allow anyone to post to the blog without an account. Unfortunately you have to then approve these posts individually. And while you can show author avatars in the “Dashboard” they don’t appear in the blog. Also, Tumblr doesn’t by default support comments and discussion. There are hacks to add this, but they are hacks.
WordPress is the best, in that you can easily see who posted what, you can have good discussion, and it not only supports Chinese text, but also has a Chinese interface. The biggest problem here is that sign up is a three step process. Students have to create an account, click on an e-mail they’ve been sent, and then give you the e-mail address they used to sign up before you can add them to the blog. You can theoretically “invite” them to the blog directly, but my experience is that this makes things harder, not easier, since if they miss that e-mail or fail to follow-through correctly, you loose track of them.
There is clearly more work that could be done to make these tools better for teaching, but for now, especially outside the US, WordPress still wins.